Carb Service and Jetting

October 26, 2012

Derbi Serviceman YellowWelcome to Myrons Carb Service and Jetting tutorial. As most of you know, the main function of a carburetor is to blend the gasoline with air to make an explosive mist of super fine droplets. In order to burn all of the oxygen and all of the gasoline, they must be in the right ratio, or else oxygen or gas will be left over, and wasted out the exhaust pipe. The carburetor also has a control valve, in most moped carburetors it is a slide type, that controls the power of the engine. When you want to accelerate, twisting the right handlebar grip towards you pulls a cable that pulls the throttle slide up. This “opens the throttle”, and lets the maximum amount of air get through. Moped and motorcycle carburetors also have a small reservoir of gasoline, called the float chamber or float bowl. An automatic valve attached to a float lets gasoline into the reservoir when the level gets too low, and shuts off the supply of gasoline when the level gets too high. The reservoir insures a fairly constant supply of gasoline, even when the demand changes as when the rider opens and closes the throttle. The float is operated by gravity, so when the bike is laid over on it’s side, and the fuel petcock is on, gas will leak out, either onto the ground, or into the air box and engine, or both. Always turn off the gas (fuel petcock at bottom of gas tank) before transporting the moped.


One or more jets dip into the reservoir of gasoline. Suction from the engine draws gasoline up through the jets. The gasoline sprays out with fairly low pressure, like with a squeeze bottle sprayer with the trigger squeezed lightly. The pressure in the venturi is less than the pressure in the float chamber, which is at atmospheric pressure, thanks to one or more vents that allow air to escape from the float chamber when gasoline comes in, and to enter the float chamber when gasoline leaves. The biggest jet is the “main jet”. The size of the main jet is what determines the fuel and air mixture when the throttle is wide open. The other jets, needle jets, idle jet(s) or choke jet, matter only a little bit when the throttle is wide open, but matter a lot when the throttle is closed. On a Tomos A55, the idle jet is about 0.010″ (0.25mm) and the main is about 0.023″ (0.58mm), 2.5 times the diameter, and 6.4 times the area. So when the throttle is wide open, 86% (6.4/(6.4+1)) of the gasoline comes from the main jet and 14% (1.0/(6.4+1)) from the idle jet. Sometimes the “idle jet” is part of the carburetor body and cannot be removed for cleaning or replacement. In those carbs, Peugeot Gurtner, Motobecane Gurtner, Delorto SHA, and others, there is a drilling procedure for cleaning, widening or relocating the idle passageway. In some there is no idle fuel passageway. Bing moped carbs use a channel in the bottom of the throttle slide to focus the air close to the fuel sprayer. Make the idle channel in the bottom of the throttle slide deeper, and the idle mixture will be richer. Make the idle channel shallower, and the idle mixture will be leaner.

Slide Carburetors Diagram

What controls mixture depends on what throttle opening is:

Closed Throttle (Idle) Mixture is usually not adjustable, except by drilling or notching the bottom of the throttle slide. 

Mid-Throttle Mixture is governed by the needle and needle jet, if it has one. Puch & Sachs Bings do, Delorto SHA doesn’t.

Full Throttle Mixture is goverened by the main jet size. The number is, somtimes, the size in mm. So a size 50 jet is 0.5 mm.

Try not to confuse throttle position with engine rpm. “Mid range” can mean the middle of the RPM range, or it can mean the middle of the throttle range.

The main jet is always removable, and unscrews from the lower part of the carburetor since it is “underwater”. In most motorcycle carburetors the main jet is internal, where the float bowl must be removed (that usually means carb removal). In some moped carburetors, it is external, like Peugeot Gurtner, Batavus Encarwi, Tomos Encarwi, and Motobecane Gurtner. Those lucky moped owners can drain their float bowls by simply unscrewing the jet. The jet can also be cleaned or swapped out in under a minute.

Above, a Tomos A55 idle jet (M4 thread) is physically bigger than a Puch Maxi main jet (M3.5 thread), but the hole size is much smaller. The photo shows how the #25 jet, 0.010" (ten thousandths of an inch), will allow the thinner wire of the wire wheel to pass through the hole, but not the thicker wire of the wire brush. This is a useful cleaning technique.

Above, a Tomos A55 idle jet (M4 thread) is physically bigger than a Puch Maxi main jet (M3.5 thread), but the hole size is much smaller. The photo shows how the #25 jet, 0.010″ (ten thousandths of an inch), will allow the thinner wire of the wire wheel to pass through the hole, but not the thicker wire of the wire brush. This is a useful cleaning technique.

With most stock moped engines, it’s easier to judge whether the jet is too big or too small, than it is with high performance two stroke engines, like dirt bikes. A stock moped with the correct jet will run smooth up to and a little beyond the engine rpm it is designed to max out at, and then, above that rpm, begin to “four stroke” or run rough. You want it to just barely not four stroke under most conditions.

If the jet is too big, the “four stroking” will begin too soon, before maximum speed is reached, and act as a brake.

If the jet is just right, the “four stroking” will begin a little above max speed , going downhill or wide open stationary with the tire off the ground. If the top speed is 30mph, the four stroking should begin at 33-34mph. If the top speed is 35mph, the four stroking should begin at 38-39, and so on.

If the jet is too small, the “four stroking” will begin too late or not at all, even above top speed. Furthermore, if the jet is too small, power will fade out, without any roughness or stumbling, like a “waaaaaaah” sound, when the throttle is opened fully. This condition will cause excess heat, which can then damage the piston or worse. A little too hot is when the two stroke chrome exhaust header turns yellow. Way to hot, for a two stroke, is when the chrome turns blue, like a four stroke exhaust header often does.

Carburetor Replacement. When starting from “scratch” with a whole different carburetor or a different engine set up, the tuning books all say to start with a jet that’s too big and work down. Putting too big a carburetor will make it difficult or impossible to jet properly. When the carb is too big, you cannot make as much power at full throttle as you can at part throttle. There’s not enough suction from that little 50cc piston. Piston port kitted mopeds can benefit from big 20 to 24mm carbs. Reed valve 70cc kitted mopeds and non kitted 50cc sport motorcycles and scooters benefit from smaller carbs, 16 to 20mm. Smaller carbs start easier, idle better, they’re more fuel efficient, they take up less space and don’t stick out as much. The big carb might go a little faster but behave badly. 

Seat of the pants jetting is where you use a public street run the bike at maximum power for maybe 1/2 mile to 5 miles (eventually), listening to the sounds and feeling the forces made by the engine, to decide if the jet needs to be bigger or smaller. Each engine has it’s own personality. Some you easily hear the four stroking, and some you cannot hear it at all, but you can sort of feel it literally in the seat of your pants, like someone tapped the brakes. When the rough running mode begins the driving force suddenly drops, and you begin to loose speed. When the rough running ends and the smooth running begins, you suddenly feel a tiny surge of power, and your speed begins to increase. Seat of the pants jetting is also knowing the smell of “too hot” and how to judge how hot it gets by “reading” the spark plug. The hottest thing in the combustion chamber is the center part of the spark plug, the insulator, made out of white porcelain. On a normal spark plug there will be a light brown coating. On a hot running bike the same plug will be a lighter shade or almost white. On a cold running bike the same plug will be a darker shade of brown. Many other things also influence the spark plug insulator color, and can mask the effect of jetting, such as two-stroke oil mix type and ratio, old gas tank tar, compression leaks, spark plug heat range, and various engine modifications. For this reason a digital temp gauge is recommended. High tech jetting is done using full instrumentation like temperature sensors, exhaust oxygen sensors, in addition to a dynamometer. Graphs of engine rpm versus rear wheel driving force/torque/horsepower, are made for various jet sizes.  The jet that provides the most driving force yet still runs cool is the best choice. What is cool?  Below 300 degrees fahrenheit at the threads of the spark plug, after 30 minutes of hard running on a super hot day. What is hot? Above 350 degrees, also when fully hot. Having too much compression ratio (not enough combustion chamber volume) is a common source of excess heat in modified engines. So is too much ignition advance. Liquid cooled two stroke motorcycles run cooler, like under 250 degrees F. Cooler engine temperature makes more power because the crankcase can hold more weight of air since cooler is denser. That’s why all modern racing two stroke engines are liquid cooled, more power and longer life. Bigger cooling fins run cooler on air cooled, as do bigger radiators on water cooled. Moving fast through the air cools the engine. Going slow in the sand, or uphill with a heavy load on a hot day, overheats the engine. Because of all the many variables, jetting is often not easy. The bike must be otherwise in good working order and street legal, before the final jetting is done.

When just an exhaust is changed, from stock to aftermarket, usually the jet needs to be 1 or 2 sizes bigger. When the air box is removed the jet needs to be 2 or 3 sizes bigger. Some mopeds are missing their air box, and a replacement is not available. They must be jetted richer, or they’ll run hot and lose power when the throttle is wide open.

Sometimes the jetting can be adjusted by different air inlet tubes that plug into the air box. They are for noise reduction. The Delorto air boxes have two 1 inch by 3/8 inch plastic inlet tubes. When they are removed, and a bigger jet is installed, some more power is often gained, at the expense of more noise and less fuel economy. For example, a stock Garelli has a #50 jet with intake restrictors. Remove one of the two inlet tubes and it likes a #52 jet. remove the other and it likes a #54 or 56 jet. Speed might gain from 30 to 32 mph. Another example is the “snorkel tube” on the Puch Maxi stock air box. It should never be pushed up against the metal mesh air filter inside the air box, but rather be placed about a half inch away from the metal mesh, or else the air will be very blocked. Puch changed that design in the mid eighties and made it fool proof. Removing that accordian style inlet tube lets more air in, about equivalent to reducing the jet size by one or maybe a half step.  

When an engine that is jetted correctly for a low altitude is moved to a high altitude, like from sea level to 6,000 feet, the air is thinner, so the jet will need to be smaller by 1 or 2 sizes. At 8000 ft maybe two sizes smaller. The power output will be less.

When an engine has leaking crank seals it will need a bigger main jet and a much bigger idle jet, because some of the fresh charge will escape, while some fresh pure air will enter the crankcase, diluting the mixure. At lower rpms, due to momentum, the leak has more time to happen, so the engine will feel weak. At high rpms the weakness won’t be that bad. One trick is to cut a notch in the throttle slide to cause all the idle air to pass close to the idle hole where the gasoline sprays out. Notching the throttle slide enrichens the idle mixture to compensate for air leaks in the crankcase, and compression leaks in the piston and cylinder. The notch can be filled with epoxy to restore it, or the throttle slide can maybe be replaced, to undo the modification. If there’s an idle passageway, it can be made wider, by drilling, to make the idle mixture richer. A Delorto SHA idle hole is in the zinc body below the base of the vertical brass spray tube. It is stock about drill size 73. It’s common for an air-leaking older engine to benefit (idle better) by widening the Delorto SHA idle hole to drill size 71, and even all the way up to drill size 68. When the engine has low suction, the idle hole needs to be huge or else it won’t idle. The droplets then are bigger and the idle is rougher. It’s either that or it’s an expensive engine overhaul or new engine. 

 Carburetor Service

Wear eye protection. Read warnings. Carb spray is a strong solvent. It will damage paint and most plastics, as well as human flesh. Carb dip is also a mix of strong chemicals that will burn skin, cause blindness, or mess up your nice new paint job. Use caution. These procedures are not for everyone. Use your own judgement. Read and follow the warning labels. Use this at your own risk. It’s easy to do more harm than good.

One little flake of this white crust became lodged in the float vent hole, causing this almost new Puch carburetor to leak gas, and to starve for gas, for no apparent reason.

One tiny flake of this white crust became lodged in the float chamber vent hole, causing this almost new Puch carburetor to leak gas, and also to starve for gas sometimes, for no apparent reason.

A quick clean is to remove the float bowl, keeping it vertical so as to not spill the gasoline it contains. If the carburetor has no been cleaned recently it might be all coated with brown or yellow varnish or white zinc oxide corrosion. If it is then a full clean is needed. If the carb is already clean inside, then inspect the gasoline for several possible contaminants. One tiny spec or fiber is all it takes to block a jet hole. See Gas Tank Cleaning section. Remove the jet and hold it up so your eye is looking through the tiny hole, with like a sunny white wall in the background. A normal jet will be wet with clear liquid that tranmits light. Blow air near it lighty with your mouth. Now the liquid will be gone. It should look like a solid white circle. A blocked jet will be black, and a flake or a fiber will make the hole look non-circular. Be aware of reflections from the brass walls. Clean out the jet, if it is blocked, with a piece of thin wire, like from a wire brush or the smallest guitar string. Better yet use a jet drill of a slightly smaller size, as a tiny round file, to scrape off the varnish from the inside of the hole. See the Bing or Delorto Jet Sizes Charts for drill numbers and jet numbers conversions.

A full clean is to disassemble the carburetor, separate out the rubber parts, and then soak the carb body and non-rubber parts in carb dip, or spray them with carb spray and maybe scrape the float bowl with a pocket knife or with steel wool. Polish the float seat with a spinning Q-tip on a drill. Clean out and test spray the passageways. Be careful not to spray it at your face. Look up the specific layout of your carb to know where any “secret” holes are at. Spraying up from where the main jet goes should cause spray to come out all available verturi holes, sometimes one, two, or three, depending on the carburetor.

How to fix a broken ”carb elbow”: The carb elbow is a curved metal tube that redirects the throttle cable at the top of the carburetor. Not all moped carburetors have a carb elbow. Instead they have linkage, like Peugeot 103 and Derbi DS50. Without a carb elbow, the throttle cable would go straight up, and interfere with your leg when you step through the frame to get on the bike. Without a carb elbow, the throttle cable would be different, since there’s length missing from the outer stationary part of the throttle cable. Some carb elbows have threads and screw into the top of the carburetor. Some don’t have threads and just rest in a hole in the carb top. The threaded kinds often get broken, usually by getting kicked. Fortunately, there’s an easy and free remedy.

Above left, unbroken and broken carb elbows removed. Above right, unbroken and broken carb elbows installed.

Usually it breaks at the bottom of the lock nut, leaving a few good threads where the lock nut was. Eliminate the lock nut and possibly file the broken edge if it sticks out. Then screw the broken carb elbow into the carb top, without any lock nut. Then turn the adjuster at the other end of the carb elbow, if it has one there, to take up the slack caused by the missing section of the carb elbow. Lube the throttle cable before reassembly.

How to fix a sticking throttle: Be aware this is a potentially dangerous condition. Don’t let anyone ride the bike until it’s fixed. Lube the throttle cable, and throttle sliding block, if it has one. Visually check the cable for kinks, or too many bends, or a crushed spot. Straighten out any kinks and remove excess cable ties. The cable should go as straight as possible, yet not hang out or dangle. If it hangs out it can get caught, and either kinked or crushed by the steering stop. Routing needs to be near the steering tube of the frame, so that when the steering is turned, it does not affect the throttle. Look at the original factory photos of mopeds in Myrons Moped Encyclopedia, to see how the throttle cable is supposed to go for your particular bike. It might not show it or say it all the way. If it still sticks try moving the throttle further out on the handlebar. Sometimes when a moped falls over, the throttle gets pushed inward, and rubs on the end of the handlebar. If that’s not it, then disconnect the throttle cable to isolate the throttle control from the throttle cable. Pull on the throttle cable with your fingertips or a small pliers. It should feel free and smooth, not rough or raspy, and snap back freely. Then twist the throttle control. It should also move completely free, like a wet ice cube on a smooth table. Replace the throttle cable with a modern kind with a slippery lining of nylon. Some throttles clamp onto the handlebar, and some have a cone shaped wedge that digs into the handlebar. After usually thousands of miles, a wedge type throttle might get loose because of erosion of the handlebar. Then tightening the wedge bolt can cause the throttle to stick because it becomes misaligned. The remedy is to replace the handlebar, or the free and easy option, reposition the throttle a little (1/2″) further out, on a fresh section of handlebar. Finally, sometimes when you change handlebars, the new bars might cause the throttle to stick, either because the throttle is misaligned by being positioned on the part of curved section, or the handlebar is too thick, like some powder coated ones are, and the thick paint needs to be sanded off where the throttle twist tube rubs against it. If you changed to low bars, without shortening the cables, it might be from the four extra 90 degree bends, where the cable has to turn up, u-turn over the top, and turn horizontal again at the bottom of the roller coaster. Sometimes throttle sticking is caused by too much grip glue. Sometimes it’s from a worn out sliding block. Allways lube cables and throttle first, and every so often, but not with WD40. Use oil, grease, or cable lube. Vegetable oil or Vasoline is better than WD40. WD40 is a penetrant and a Water Displacing agent. It’s great for the first time, because it gets in deep and fast, but doesn’t last long. Regular motor oil is better for follow up lubing.

 

to be continued … fuel leaks and remedies, troubleshooting with carb spray

Myron Derbi Goodwrench wishes you a safe, happy and successful carb service.

Service Basics

September 5, 2012

CONTENTS:  Welcome   1  Reading List   2  Owners Manual   3  Spark Plugs   4  Service Manuals

5  Tire Mounting   6  Threads   7  Seized Engine

Welcome to Myrons Service Department. Mopeds are easier to work on than cars. You don’t have to lay under them and get dirt in your eyes and oil in your hair.

Myrons Mopeds has stopped doing most moped service, except for new Tomos. That has made things difficult for many people. So here and throughout the website, plenty of useful information is provided, or is being planned, to help people repair mopeds and find parts. Things like how to cut a hole and install a universal bulb socket in a burned out metal backed headlight bulb to recycle it. 

To begin, here are some good introductory and non-specific service articles to read first.

1 Moped Repair Basics – Reading List – Links:

Fred’s Guide – How to Fix your Moped: http://www.mopedriders.org/article_view.php?faq=2&fldAuto=8  Read this first to build a foundation of general knowledge. Highly recommended.

Minarelli Service Manual: http://www.mopedriders.org/article_view.php?faq=2&fldAuto=23  Read page 17 and 18, Two Stroke Engine Theory. 

Moped Repair Handbook: http://www.mopedriders.org/html/manuals/dempsey/dempsey1and2.pdf  These are the first two chapters of an excellent book by Paul Dempsey, Nov 1977. Very highly recommended.

Moped Army – Wiki – Repair Tutorials:  http://www.mopedarmy.com/wiki/Category:Repair_tutorials  Hundreds of good user supplied articles on many service topics. Pick and choose what you want to read about.

There are also many good moped service videos on YouTube.com.

2 Moped Owners Manual  – General Information – Basics

by Shaun Strahm, Myrons Mopeds, 1879 W Commonwealth #L Fullerton CA   714-992-5592   Dec 1999

TWO-STROKE ENGINES:

Mopeds have two-stroke engines. Outboard boats, chain saws, weed wackers, and many small motorcycles also have two-stroke engines. It’s called “two-stroke because the spark plug fires every two strokes of the piston (down & up). Four-stroke engines, like cars & lawnmowers have, fire the spark plug every four strokes of the piston (down, up, down, up). This is why two-stroke engines sound more like buzzing insects, while four-strokes sound more like a drum roll.

Two-stroke engines run on gasoline with two-cycle oil mixed in, or have oil injection. A two-stroke engine does not have motor oil in the crankcase, like a four-stroke does. Instead the crankcase contains the gasoline and air mixture, with a little bit of two-stroke oil added in. After the two-stroke oil coats the crank bearings and piston it is burned along with the gasoline. The burning of oil makes a little bit of smoke in the exhaust, which is normally barely noticeable.

TWO-STROKE OIL:

The most important thing you can do to keep your moped healthy is to use a good quality two-stroke oil and mix it in the correct amount of 50 to 1 (2.5 ounces per gallon). This will make the engine stay strong and last a long time, and help prevent carbon build-up inside the exhaust. The oil we sell and recommend is called Champion 2-Cycle Oil and comes in small 2.5 oz bottles for $2, and large 12.5 oz bottles for $5. Some of the highest mileage mopeds I have seen over the years have used this oil, which is a petroleum based oil with expensive synthetic additives. Pure synthetic oils are also very good. You buy good quality two-cycle oil at motorcycle and lawnmower shops. Auto parts stores usually only carry ordinary less expensive blends. Grocery and drug stores also carry cheap two-cycle oil.

OIL INJECTION:

If your moped has oil injection, then you don’t have to mix oil in the gas. Instead you add two-stroke oil to an oil tank located usually under the seat. A small oil pump squirts about one drop of oil every few seconds into the intake port, where it is ultimately burned up. The oil gets used up as you go, and so the oil tank must be refilled every so often, usually about every 3 gas fill-ups (300 miles). If the oil tank is allowed to run out of oil after a few minutes the engine
will seize up and suffer piston damage.

OIL & GAS MIXING:

The best way to mix the oil and gas is with a gas can. If you have a small pill-bottle-size 2.5 ounce bottle of two-stroke oil, you just pour that into an empty one gallon gas can and then take the gas can to a gas station and put one gallon of gas in it. By adding the oil first you have eliminated the need to shake the gas can afterwards, because the force of the gas pump has already stirred up the mixture and dissolved all of the oil. If you add the oil last it will at first settle at the bottom, and the gas container must be sloshed around a few times. Two-stroke oil is usually colored green so that you can see the green tint of pre-mixed gasoline. Without shaking or stirring the gasoline would be dark green at the bottom and clear at the top. Once the oil dissolves the color becomes very light green throughout, and the oil will stay dissolved and never settle out so there’s no need to ever shake it up again.

The other way to mix the oil and gas is directly into the gas tank. Most moped gas tanks hold about one gallon maximum and they usually don’t get below 1/4 gallon before they’re refilled, but the tank should not be filled all the way to the max because of gas leakage out of the gas cap vent hole, so the actual amount of gasoline needed to refill is usually about 1/2 to 3/4 gallon. If you buy 1/2 gallon of gas then you need 1/2 of a bottle of oil. If you add the oil just before adding the gas, it will be mixed automatically by the force of the gas pump and you won’t have to shake the bike up afterward. If you add the oil last then just make sure to shake the entire bike sideways and back and forth to splash around all of the gas in the tank. Always do this with the kickstand up so you don’t bend the center stand.

You should carry with you a small 2.5 ounce bottle of Champion 2-Cycle Oil that’s enough for one whole gallon. Most mopeds have a compartment that holds a small bottle of oil, which you keep refilled from a big bottle you keep at home. That way you always have oil with the bike. You cannot add gasoline and then drive home and add the oil later because after about two minutes of running without oil the engine will seize-up and damage to the piston, rings, and cylinder walls will occur.

A lot of people ask if it’s better to use too much oil than not enough. The answer is yes but too much oil, say 5oz/gal, can foul the spark plug causing the engine to not run or start until a new spark plug is installed. Way too much oil in the gas, say 10oz/gal, will clog the carburetor and the engine won’t run until the carburetor is cleaned out. Too much oil causes excessive exhaust smoke and leads to premature muffler clogging. Not enough oil, say 1.5oz/gal, will not hurt a normal moped that’s driven slowly. For all these reasons its best to use 2.5oz/gal and never less than 2.0 or more than 3.0.

GAS VALVE:

All mopeds have a gas shut off valve at the bottom of the gas tank. The valve knob has three positions, OFF (closed), ON (open), and RES (reserve). You should always keep the gas valve OFF when you’re not using the moped, or else gas can leak out of the carburetor. If the gas is left on, it’s up to the float valve inside the carburetor to stop the gas from leaking. On a new bike or one that has a good working carburetor float the gas valve can be left on for days without any
leaking. Moped carburetors hold about 5 spoonfuls of gasoline, enough to go about a half a block. So if you forget to turn the gas valve on the bike will start and run for about one minute and then stop running. Turning the gas valve OFF and running the engine until it uses up the 5 spoonfuls of gas in the carburetor is what you should always do before transporting or storing the moped.

The RES (reserve) position is for when the tank is very low or getting near empty. The bottom two inches of the gas tank does not come out when the gas valve is ON. So if youre going along and the gas gets too low it will “hit reserve” and run out of gas. Then you can switch the gas valve to RES and start heading towards a gas station. On most mopeds the reserve is enough to go a few miles. You can run on RES all of the time, but its recommended to use ON instead because it does not draw gas from the very bottom of the tank where rust powder and water tend to settle at. Most gas valves are marked or labeled. In case yours is not, OFF is almost always to the right as your facing the valve, ON is always down, and RES is either to the left or up.

BACKWARDS KICK STARTING (TOMOS ONLY):

Tomos mopeds since 1976 have always had way of starting that’s different from all other mopeds. On a Tomos you kick either pedal backwards to start the engine. On all other mopeds you kick either pedal forward while pulling a lever. Also unlike all other mopeds, a Tomos does not need to be on the center stand when doing a stationary kick start. You should always have your left hand on the rear brake lever when stationary starting off the center stand. On a normal Tomos you don’t need to give it any throttle at all, but if you do give it throttle, when it starts it will immediately lurch forward. Holding the left (rear) brake on prevents the bike from moving forward before you’re ready. 

KICK STARTING:

Put the moped on the center stand so that the rear tire is off the ground. If the bike has a bent or worn out center stand or if there’s too much weight on the back it will not be able to start this way, because the rear tire must kept from touching the ground. Stand on either side of the bike with both hands on the handlebars. Turn the pedals backwards until the one on your side is almost straight up.

A. LEFT START LEVER ENGAGES MANUAL STARTING CLUTCH, used on the following mopeds:

Puch, Sachs engine, Minarelli engine, Morini engine, Garelli, Batavus, Trac, Foxi, and others: Pull start lever on the left handlebar and push the pedal down while holding the start lever. When the engine starts let go of the start lever.

B. LEFT START LEVER IS DECOMPRESSION, AUTOMATIC STARTING CLUTCH:

Derbi, Vespa, Honda PA50 Hobbit, Kinetic, Trac (Dai Lim engine), Angel, and others: On these mopeds there is also an engage lever either on the engine (Derbi only), or rear wheel, that disengages the rear wheel from the motor, so the bike can be pedaled or pushed without the automatic starting clutch trying to start the engine. Pull the decompression lever and push the pedal down. As your foot is going down, let go of the lever. The engine will start the moment you let go of the decomp lever.

C. RIGHT START LEVER IS DECOMPRESSION, AUTOMATIC STARTING CLUTCH:

Motobecane & Peugeot only. Same as Type B, except decomp lever is on the right side handlebar. The left lever is a choke on these French made mopeds. These mopeds have an engage switch on the belt pulley that disengages the rear wheel from the motor, so the bike can be pedaled or pushed without the automatic starting clutch trying to start the engine.

In all 3 types A, B, & C, you should always have your left hand ready to squeeze the left (rear) brake lever in case the rear tire touches the ground while its turning fast.

PEDAL STARTING:

If you are already on the bike and it’s off the center stand you can start it by pedaling up to about 5mph and then pulling the start lever while continuing to pedal. If your moped has a decomp lever then you pull it first, then pedal, then let go of the decomp lever. Pedal starting is the only way to start a bike that has a bent center stand or too much weight on the back. If the pedals are not working the moped can be push started by walking it forward instead of pedaling.

                                   3 Spark Plugs

Spark Plugs are important. They’re also cheap and easy to change. The spark plug is the first thing you look at when a motor won’t start. Spark, compression, and fuel are the three main ingredients. Spark plugs come in different sizes and styles. See Parts Department to learn what sizes and styles there are.

Reading spark plugs: The condition of the spark plug tells you about the condition of the engine. A normal spark plug has a light brown coating on the white porcelain insulator, and sharp corners on the center electrode. A high mileage spark plug in a healthy engine looks the same but the electrode corners are rounded. Sparks like to jump from pointy things. A rounded center electrode or way too big a gap might make the engine hard to start. 

Checking for Spark: Remove the spark plug, connect the cap to it, and lay it on the engine so the metal shell touches the engine. Turn the engine over either by pedal starting or by flicking the flywheel with your hand. Little momentary light blue sparks should be jumping the gap, making a “snap” sound each time the piston goes up and down. Modern CDI ignitions are hard to see in bright sunlight, so check for spark in the shade. A bright white, pink, or yellowish spark is bad. That usually indicates a fouled plug. Dim and blue is good, especially if the snap snap snap sound is loud.     

4 Free Service Manuals for Viewing:

Almost All Kinds – General Moped Repair – Large List of Online Moped Manuals:   http://www.mopedriders.org/article_cat.php?fldAuto=2&sid=21a224ebbb5dba61c6cb0fd180fbbd60  Wow! A collection of useful manuals: Avanti, Batavus, Casal, Cimatti, Garelli, General, Honda, Jawa, Kreidler, Minarelli, Morini, Motobecane, Murray, Peugeot, Puch , Rizzato, Sachs, Tomos, Yamaha, Zundapp. Big thank you to MRA!

Batavus Moped – Owner Service/Repair 1976-1978:  http://www.mopedriders.org/html/manuals/batavus/csm/batavuscsm.htm  Covers Batavus one-speed mopeds with the Laura M48 engine. For home mechanics, by Clymer Publications. All Clymer manuals have a good Chapter 1. General Information, and Chapter 2. Basic Hand Tools, before they get into the main course.

Derbi 49cc Flat Reed “Start” Engine 1986-1989:  http://mopedcentral.com/images/DerbiEngineRepair.pdf   What was the king of US model mopeds, the Derbi Variant Sport and it’s cousin the DS50. This was their factory (engine only) service manual. There was nothing else but parts manuals and wiring diagrams for the 1986-1989 Derbi’s.

Garelli Moped – Owner Service/Repair 1976-1978:  http://www.mopedriders.org/html/manuals/garelli/csm/garellicsm.htm  Covers one speed and two speed Garelli mopeds from the 1970′s and 1980′s. For home mechanics, by Clymer Publications. Good quality.

American Garelli Service Manual:  http://www.mopedcentral.com/images/AmericanGarelliServiceManual.pdf  Excellent factory service manual for 1970′s and 1980′s (USA models with brake light and horn) Garelli mopeds with the Garelli one speed automatic 49cc horizontal cylinder engine.

Motobecane Repair Operations – Models 40, 50, 7:  http://www.mopedriders.org/article_view.php?faq=2&fldAuto=18  This is the real thing, with five pages of special tools at the beginning. Let that be a hint that Motobecane does things their own way. The bike may be hard to work on, but the manual is well written.

Peugeot Moped – Owner Service/Repair 1976-1978:  http://www.mopedriders.org/html/manuals/peugeot/csm/peugeotcsm.htm  Covers Peugeot 103,  US models, from 1976 to 1980. For home mechanics, by Clymer Publications. Good quality.

Puch 1980-1981 Service Manual : http://www.mopedriders.org/html/manuals/puch/sm/puchsm.htm  The best Puch moped factory manual. Covers 1970′s models as well, one-speed and two-speed.

Tomos A35 Service Manual:  http://www.tomosmopeds.org/forum/showthread.php?2145-A35-Service-Manual This is the Tomos factory manual for the early two-speed A35 engine 1991-1993 that had points ignition and the carburetor in the center. The rest of the info applies to the later A35 engines 1994-2006. The transmission info applies to the A55 engine 2004-later. Excellent technical drawings, specs and procedures.

Tomos Streetmate A52/A55 Information and Tuning Manual: http://www.tomosforum.nl/uploads/Pim/Tomos_Streetmate_A55_-_Information_and_Tuning_Manual.pdf  This is a technical masterpiece, the best and most complete. By R.L. Vuyk. From the Netherlands, where mopeds rule.

5   Tire Mounting

This is not a complete set of instructions. You can read how to change a moped tire in most manuals. This is an additional item, very often overlooked that needs mentioning.

Left,  a tire has just been mounted on the rim. Before air is added, the area near the valve stem is checked. Sure enough, the tube is pinched between the tire and the rim. If ignored, this will cause a bulge in that area.

Right, the same tire after pushing the valve stem up inside the tire. Now the tire will be straight when inflated. Pushing the valve stem inside the tire before the final mounting will also make the mounting easier, since the pinched inner tube is making the tire tighter on the rim on the opposite side. When your tires are mounted correctly, smooth roads will not feel like bumpy ones, and your bike will feel solid, smooth, and more enjoyable.

6  Threads

Here are several views of Myrons Thread Pin Cushion:

 Read all about threads here: http://www.parktool.com/blog/repair-help/basic-thread-concepts.

 

7 Seized Engine: How to unfreeze it

A seized engine is when the crankshaft, rod, and piston are frozen solid and cannot move. You try to pedal start it and it acts like a brake when you pull in the start lever (on a manual starting clutch type), or when the automatic starting clutch engages. It never makes that chug chug chug sound of the piston going up and down.

Here are the steps to diagnose and/or recover from a seized engine.

1. Spray WD40 into the spark plug hole. This will get solvent to the piston top and cylinder wall above the rings. If the piston is just stuck with tar from sitting, this will dissolve some of the tar and maybe unfreeze the engine.

2. Spray WD40 into carburetor (after removing the air filter) with throttle held wide open. This will get oil into the crankcase and lower part of the piston and cylinder, below the rings.

3. Locate the flywheel. Some bikes it’s on the left and some it’s on the right. The magneto flywheel on a moped is a 4 or 5 inch wheel that has magnets inside it. Most have wide holes that allow adjusting the points. The flywheel is attached directly to the crankshaft. It is crucial to not confuse the clutch wheel (which turns with the rear tire) with the flywheel (which turns with the engine). Motobecanes and Peugeots have exposed “wheels” on both sides on the engine.

4. Try to rotate the flywheel with both hands. If it moves, try going back and forth, each time a little more, until it goes all the way around. Then spray more WD40 in and go around again many times. When it’s loose enough, switch to pedalling to rotate the engine faster than by hand. When it’s finally free, it will not feel tight anywhere (with the spark plug removed). A normal flywheel that’s “free” should move in a full circle with one strong finger. If it takes a whole hand then it’s “tight”, not “free”. 

5. Determine what is stuck. A small screwdriver in the spark plug hole is used to feel the top of the piston. When just the piston is stuck, the crank will move a tiny bit back and forth, but the top of the piston will not move at all. When something like a loose screw or piece of debris gets stuck in the flywheel, the flywheel might move free within a range. Then the top of the piston will move with the crank. When neither the piston nor flywheel moves at all, then remove the flywheel and try to rotate the crank. If the naked crank is does not move, the engine is stuck internally, and the flywheel will then need to be put back on tight to continue the unfreeze process. If the crank and piston move free, then the flywheel is rubbing or sticking somehow. That can be caused by several different things each with a different remedy.

6. Find or make a tool to hold onto the flywheel, once you’re sure it’s stuck internally. Be careful to not allow the tool to damage the coils or wires behind the flywheel. Apply a rotation torque of, perhaps, 150 ft-lb for an 8mm crank nut, or 200 ft-lb for a 10mm nut crankshaft. These are estimates only. Be advised that too much torque can shear off the woodruff key and/or damage the crankshaft and/or flywheel woodruff key groove, or even break the crankshaft (possibly $500 damage). Applying high torque is risky but beneficial. 

To be continued …

 

New Tomos Transmission Service

August 31, 2012

Basic A35/A55 Transmission Service

Replacing the first speed clutch segments:

1. Once the transmission oil is drained out, and the trans cover removed, the clutch and trans are exposed.

2. The 17mm clutch nut is spun off with an impact wrench. The outer first speed clutch just pulls straight out.

3. The circular coil spring is removed. The old clutch segments are removed, preserving the orientation.

4. The new clutch segments are transferred over one at a time so as to not scramble the direction.

5. The three leaf springs are put back, with tails inside, not outside the neighbor spring’s cradle.

6. The circular coil spring is carefully stretched and maneuvered into position. See photos below.

Step 6a. Getting everything ready for the spring pre-loading (stretching).

At the gaps between the segments, the leaf springs have “cradles”. These cradles prevent the spring from wandering either way and coming off. When installing, always put the c-clamps or vise grips where you can almost get two of the three cradles. Never clamp onto the spring or the brake lining. Left, initially set the clamps like this. There’s no tension in the spring yet.

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Step 6b. Gently stretch with soft thumbs then clamp it

Now with both your thumbs, gently stretch and lift the spring onto the ledge, but not yet over the cradle. You cannot let go or it will come off and maybe fly away. Hopefully you have a third needle nose vise grips within arms reach that is already adjusted and ready to clamp. Without letting the spring snap back and without taking too much time, clamp the third vise grips (a needle nose vice grips like shown here is best) to prevent the spring from flying off.

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Step 6c. Gently pry the spring over the cradle with a small screwdriver

Just like putting a tire onto a rim, that last little bit is the most difficult. It’s very easy to damage the spring by forcing it to go when it doesn’t want to. If it gets tight, release and try to take a smaller bite. If the new spring is over stretched by rough handling during installation, it will be like having an old softer one.

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7. Once it snaps over the cradle you got it. Now just push on it to snap it in it’s groove all around.

8. Place the assembled 1st speed clutch back on, tighten the nut with the impact.

9. Put the two rear shaft’s shim washers 10 & 16mm in place, clean the gasket surfaces and any sludge.

9a. For Pedal Models:  Take the left pedal crank off, or at least park the pedal in the down position. The weight of that far side pedal makes the pedal shaft point wrong, causing the transmission cover to not go on right.

9b. For Pedal Models: Make sure the U-shaped clip is in it’s slot in the case wall. The starter (pedal) shaft should move 45 degrees back and forth. If only the clutches were removed, and not the countershaft and pedal shaft assemblies, then it will still be in it’s slot, ready for the trans cover to go back on. More pictures of this will be put here soon …

10. Put the trans cover on. When everything is aligned, it makes a loud clap.

11. Then tighten the trans cover bolts. Put new ATF fluid and go try it out!

New Tomos Electrical

August 13, 2012

Welcome. Scroll down to the topic you want:

1) Basics of Tomos Moped Electrical Systems   Everything is Circuits, Shorts and Opens, Volts and Amps, Batteries and Generators, Magnetos, Magneto versus Battery, Testing without a Tester, Example 1: Prince of Darkness, Example 2: The Flasher, Make predictions, AC lights and DC lights, Example 3: The Double Crosser, Example 4: The Flickerer, Example 5: The No Charger

2) Tomos CDI Ignitions 1994 to present    Ignition, How to Test a Coil, How to Check for Spark, Ground the Coil Wire to Stop the Spark, Tomos  A35 and A55 CDI Ignitions, Ignition Timing, Ignition Symptoms

3) Tomos Wiring Diagrams 1992 to present.  Here are over a dozen wiring diagrams, colorized and enhanced with notes, part numbers, and additional useful information.

Basics of Tomos Moped Electrical Systems

by Shaun Strahm, Myrons Mopeds, December 2010, updated Nov 2012

The following is a “crash course” on how to find and fix electrical problems on late model TOMOS mopeds.

Everything is circuits

Every electrical system is composed of current loops or circuits. The electricity flows out, goes through the device being powered, and then flows back. That is why all electrical cords have at least two wires. One wire is out and one is back. Coaxial cables look like one wire, but they’re actually one wire surrounding another. If you follow that pair of wires in an appliance cord all the way to the transformer on the power pole, you’ll see they’re joined in the windings of the transformer, forming a closed loop.  In some electrical systems such as automobiles and mopeds, the metal frame is a “ground”. In this context a “ground” is a path for the electricity to flow through that is shared by many loops. If the cars in a big city were electricity, then each current loop would be one car, going to work in the morning and then coming back in the evening, making a loop. Then the freeway would be the ground, where the separate current loops all share the same roadway.  When several devices are connected with each having its own current loop, they are said to be connected in “parallel”. Unplug one device and the others are unaffected. Everything in your house is wired in parallel, and has its own current loop. Similarly, on a moped, the head light, tail light, brake light, and horn are wired in parallel, and have their own separate loops or circuits. The tangled nest of cords behind your computer desk, as well as the wires in your moped, can, in principle, be laid out in nice straight parallel lines in order to visualize the “scheme”. This is called a “schematic” diagram. Being able to visualize or draw the schematic is required to understand any circuit.

 

Figure 1: Schematic diagrams of a moped and a house are the same. Every device is in a “parallel” loop or circuit.

     When two devices are connected one after another, they are said to be “in series”. The only things on a moped or in your house that are in series with other things are the switches. From figure 2 below, you can see from the house wiring diagram that the TV switch turns on the TV and not the computer. You can see that the breaker turns off everything. From the moped wiring diagram you can see that the light switch turns off the lights but not the horn. This is basic.

Figure 2: The devices in a moped and a house are in parallel, while their on/off switches are in series.

You can usually tell how a moped or a house is wired from observing the behavior of all the switches and devices. Any switches must be in series with the devices they turn on and off. Each device and its (optional) switch must be in parallel so that they can be turned on and off independently of one another. This is predicting the wiring diagram from the observed behavior. Conversely, you can also predict the behavior from observing the wiring diagram.

Shorts and opens

Not every electrical problem is a “short”. The term “short” is unknowingly misused by the general public to mean two opposite things at once, a “short circuit” and an “open circuit”. It can mean a true short, where a wire (or anything that carries electricity) touches another, forming a shorter loop that redirects the electricity through the short loop and not through the original loop. Or the term “short” is misused to mean an open, where a wire (or anything that carries electricity) does not touch another, interrupting the loop and causing the electricity to not flow through the loop. Both a short and an open can cause electricity to not flow through a device, but for completely opposite reasons.

Figure 3: A “short” is a shortcut that steals most of the current from the device. An “open” interrupts the current.

Volts and amps

Electricity flowing through a wire is analogous to water flowing through a pipe. It is measured in two ways. The “voltage” (in volts), is like the water pressure (in pounds per square inch). The “amperage” (in amperes or “amps”) is like the water flow (in gallons per minute). When you’re taking a shower and someone turns on the garden hose, your water pressure drops. Less water pressure results in less water flow and your shower gets weaker. Likewise, when starting your car, all your lights get dim. This is because your 12 volt battery momentarily drops down to 6 or 8 volts when the starter motor is using up most of the available current.

Batteries and generators

There are two main sources of electricity. Batteries (and fuel cells) produce steady current, called “DC”, or direct current.  Generators (and alternators, magnetos, and dynamos), make “AC”, or alternating current. The current made by a generator alternates direction back and forth, in sync with the rotation. The rotation is what causes the electric current to be AC. All power plant generators in the USA are set to rotate at a speed that always makes 60 cycles per second AC, or 3600 cycles per minute. On a moped, the generator rotates with the engine, which varies in speed from about 1000 cycles (revolutions) per minute “rpm” at idle to above 8000 cycles per minute going fast downhill. So the “frequency” (how fast it alternates) of the AC is variable in a moped, but not in a house. Many devices such as lights, behave the same no matter what the AC frequency is. In fact an incandescent light bulb works exactly the same on AC or DC current. In figure 4 below, graphs of voltage versus time show the main types of electricity. 60 wave crests happen in about one second, so the time scale is too short for the human eye to see. Only an oscilloscope can show the “wave form”.

Figure 4: AC is from generators. DC is from batteries. In between is rectified AC or “rippled” DC.

Magnetos

Mopeds and small motorcycles have magnetos. A “magneto” is a generator plus a no-battery ignition. A magneto ignition will operate with a dead battery. Automobiles and large motorcycles have battery ignitions. They require a battery, both to operate and to start up. Dirt bikes and power equipment without lights have magnetos with a single wire output. That is the ignition wire that goes from the source coil (and points and condenser) inside the engine to the transformer coil outside the engine. All street bikes with lights have two or more wires coming out of their magnetos. One is for ignition, and the other(s) is for lights. We now focus on the lighting wires, which are normally separate from the ignition. If you turn over a moped engine, that is, cause it to rotate, then some electricity will be generated and the lights should come on while it’s being rotated. Just because the lights work does not mean the ignition works. They are like two separate generators tuning on the same shaft. As the engine rotates faster, the lights get brighter, indicating more voltage is being produced.  The magneto/generator will reach a speed where the voltage will level off. Above that speed the lights won’t get any brighter. So a magneto is self-limiting with regard to engine speed (and thus vehicle speed). The bad thing about a magneto is when you are stopped idling your lights are dim. With a battery, your lights are always almost the same brightness all the time. The good thing about a magneto is you don’t have a heavy expensive battery that goes bad if you leave it sit for over a few months.

Magneto versus battery

The most important difference between a battery and a magneto is a battery will deliver an almost unlimited amount of amps, if it is allowed to, while a magneto will limit the maximum amps by dropping in voltage. Because of this, a battery system needs fuses to protect its wires from melting from too many amps. A magneto does not ever have fuses, nor does it need them. This difference makes moped electrical troubleshooting different from automobile troubleshooting. A magneto almost never burns out or causes wires to melt. You can short a magneto’s lighting wire directly to ground, and it will only get warm. Short a battery’s positive terminal to the negative and the wire will suddenly glow red and splatter molten copper and sparks. That’s quite a difference. A battery is always “live” even when the engine is not running. A magneto, however, is only “live” when the engine is running. So when troubleshooting a magneto system, instead of starting and stopping the engine to perform voltage tests, it is more convenient to leave the engine off and perform continuity (ohms) tests on “non-live” wires. When the leads on an ohm meter touch each other, the resistance (ohms) is essentially zero. When the pair of test leads does not touch each other the resistance (ohms) is essentially infinite. Instead of watching the needle swing on a meter, a continuity tester that makes sound is better. With a tester that beeps when the leads touch, and with the leads connected to the wire being tested, you can then focus your eyes on the suspicious area and wiggle or move the wires around listening for the beep to change. When your suspicious wire touches the bad spot, the tester will beep. Or when your suspicious wire goes open, the beep will stop. This is the usual way of checking bulbs, besides looking visually for a broken filament. A good bulb will have continuity (very low ohms), while a bad bulb will have no continuity (very high ohms). You can often check a bulb without removing it from the socket, by connecting the test leads to the wires that lead to the bulb. If there are branch points along that wire that lead to other bulbs, then those other bulbs must be removed from their sockets in order to isolate the suspicious one.

Testing a without a tester

You don’t need a weatherman to know which way the wind blows. Likewise it is possible to perform useful tests with just swapping things around, unplugging things, or using paper clips or clip leads as temporary wires. When your toaster stops making toast, the first thing you do is go plug it into a wall socket that is known to work. Then if the toaster works there, you know the problem is in the wall socket. If it still does not work in the good wall socket, then you know something’s wrong with the toaster. Right there you just applied mathematical logic to perform troubleshooting. People who are good at math and logic puzzles also have an easier time solving electrical problems. The most important tool needed for electrical troubleshooting is the mushy grey stuff between your ears. Each test, when performed properly, establishes a new truth. The newly established truth forms the basis for a further test. Each successive test narrows down the possibilities, until finally there is only one possible explanation for the results of all the tests. There is almost always more than one way of troubleshooting. Instead of moving the suspicious toaster to a known good wall socket, an alternative way of troubleshooting it would be to take a known good lamp and plug it into the suspicious wall socket. If the known good lamp works there, then you know the wall socket is good and the toaster is bad. If the known good lamp does not work there, then you know the wall socket is bad but you still don’t know about the toaster.  That is the kind of precise mathematical thinking required to solve electrical problems (puzzles to some).

Example 1: Prince of Darkness

Here is a real life moped troubleshooting example. Let’s say your 2003 Tomos Sprint head light does not work. You first learn about how it’s wired from the wiring diagram. That tells you there is a head light on/off switch on the right handlebar, and a high beam/low beam switch on the left handlebar. Right away you look to see if the switch is on. If it is, then you see if switching from high to low beam matters.  On an already running bike, you would start the engine, flip the switches, and observe. If the head light worked on high beam but not low, that would mean the problem must be after the high/low switch, in the low beam (white) wire, low beam bulb socket prong, or most likely the low beam filament inside the bulb. If the head light did not work on either high or low, then nothing new is learned. Looking at the wiring diagram you can see that all of the lights work of one wire. So you would test to see if the tail light, brake light, speedometer light, and horn work. Again you would start the engine, press buttons, and observe. If none of the devices work, regardless of what position the switches are in, then it’s possible that all of the devices (head light bulb, speedometer light bulb, tail light bulb, brake light bulb, and horn) could be bad all at once. However, it’s far more likely to be a single fault in the yellow wire that supplies all the devices. There’s two ways the yellow wire can be bad. It can be touching ground anywhere along its length, from the speedometer bulb to the magneto, causing a short circuit, or it can be an open circuit somewhere before the first branching point, possibly in the magneto. Understanding that is the hardest part. The next test would be to unplug the yellow wire from the engine, start the engine, touch the yellow wire from the engine directly to ground and see if it sparks. If the generator is working, it will spark. Let’s say it does spark. Then you would look to see if it sparked when you plugged it back in, maybe using a paper clip to see sparks that might be hidden by the connector cover. If it does spark when it’s plugged in, yet none of the lights come on, it can only mean that the yellow supply wire is touching ground somewhere, allowing the current to return without going through the lights. Next step is to start eliminating the various possibilities. The AC voltage regulator is a good place to start. You would unplug it and then start the engine and see if the lights work. On a 1992-later Tomos moped you need a voltage regulator only when the engine is revved up to keep the bulbs from burning out from too much voltage (like 18 VAC max without regulator, 13 VAC max with). The lights will work fine without a regulator, but the engine must not be revved up too much. Let’s say that the test is performed, and the lights still don’t work, even with the regulator disconnected. Next possibility might be to look at the yellow wires going to each brake light switch, since they are easy to get to. Pull the rubber hoods off and let the wires hang loose, a yellow and a green on each side. Now if the brake light green wire was shorted to ground, and at the same time the yellow and green on either side were unplugged and touching each other , then the brake light would be always on, always stealing the juice from the other lights. You would start the engine with the brake light switch wires loose. Bingo! Suddenly the head light, tail light, speedometer light, and horn all work. So you would put the regulator back and then go look for the green wire touching ground somewhere. You know it must be true. You would look first under the back fender, where the tire sometimes rubs against the tail light and brake light wires. Eureka! The green wire is all shredded and touching the brown ground wire. You went from one end of the bike to the other, without any test equipment, just plugging and unplugging wires in a logical progression.

Example 2: The Flasher

In this example, a 2008 Tomos LX, turning on the right turn signal makes all the lights flash. You go to the wiring diagram and notice that all the devices run off the yellow AC power wire. You reason that if the purple wire, which is for right side turn signals, is shorted to ground somewhere, then that would explain the bad behavior. Whenever the right side turn signals would try to go on, the short would steal the current away and make all lights go off. The turn signals are plastic and almost never get shorted internally. It can happen from someone bending the prong that touches the bulb, so that it touches the bulb socket. But more likely, the purple wire is touching ground somewhere under the back fender. After looking under the rear fender and seeing no signs of wire damage from rubbing on the tire, you would start performing tests to isolate the problem. You would unplug both right turn signals. The problem would go away if it was in one of the turn signals. But it doesn’t. You study the wiring diagram and notice there are many ways you can unplug things on a 2008-later model. You might choose to unplug the main plug. From looking at the wiring diagram you would know that the front turn signals and indicator light would be eliminated, but the rear turn signals would still try to function. You perform the test, and lo and behold, the problem goes away. This means that the purple wire is touching ground somewhere from the main plug forward. You would then maybe look at the front harness where it goes up under the gas tank. A normal 2008-later Tomos Sprint, ST, or LX has the three electrical bundles and the two control cables (throttle and rear brake) distributed evenly on the right and left sides of the steering tube part of the frame. Some 2008-09 bikes came from the factory with all of the wires and cables on one side. This makes it very difficult to get the cable tray on and very likely to pinch or puncture the wires with one of the cable tray screws. You notice that your bike is like that, with the cables and wires all on one side. You loosen the cable tray screws, letting the wire bundles dangle. You plug back in the main plug and start the engine. The problem goes away. Then you notice the snake bite puncture wound the cable tray screw made in the front wiring harness. The permanent fix is to unplug the main plug, and the right switch plug, and relocate the front harness and right switch harness to the empty left side. So the right side should have the throttle cable, rear brake cable, and the left and switch harness. The left side has the hefty front harness and the slim right switch harness. With this proper routing the cables and wires almost never get damaged.

Make predictions

The troubleshooting process involves making predictions. Look at any of the Tomos moped wiring diagrams in the collection. Imagine cutting a wire or two, here or there, or touching one or more to ground. In each case a good technician should be able to predict the misbehavior of all the lights and devices for all possible cases, just by looking at the wiring diagram or visualizing it in their head. If you study each of the eighteen Tomos moped wiring diagrams in this collection and imagine what would happen when any given wire becomes open or shorted, then when you do see the real life misbehavior, you will often know right away what the possible causes are, since that scenario has already been rehearsed. For example, ask “what if the blue (high beam) wire touches ground”. Answer “all the AC lights would go off, but only when the high beam is turned on”.

AC lights and DC lights

The deluxe Tomos “battery” models, 2001 and later, including Revival and Streetmate, have both 12 volt AC and 12V DC electrical systems. Like the regular models (Sprint, ST, LX), the “battery” models use the 12V AC generator/magneto for the head light, speedometer light, and tail light. The other lights and devices, which are the brake light, turn signals, horn, oil light, and electric starter, are powered by a 12V DC battery.

Example 3: The Double Crosser

<Under construction>

Example 4: The Flickerer

On 1991-2008 Tomos A35 and 2007-2008 A55 models, excluding Revival and off road, the CEV switches are integrated into the lever and throttle housings, and cannot be unplugged from the wiring harness. To replace these switches, each wire must be carefully un-soldered and re-soldered. A micro-tip low wattage soldering iron is needed to reach in, and to not melt the black plastic housing. Sometimes when trying to not overheat the switch plastic, the solder joint is made “cold”. This is where the solder is “balled up” rather than “blended in”, where it is stuck only by the flux and not the solder. Here, the blue hi-beam wire is a “cold” solder joint. When you wiggle the wire it causes the high beam to flicker. The remedy is to re-solder it.

 

 

 

 

Example 5: The No Charger

This 2009 Tomos stator, back side,  had this wire, green arrow, smashed flat against the aluminum wall of the stator plate. It was not touching all the time. The coils do not look overheated.

This machine was a 2009 Tomos Streetmate-R, a “battery model”. It’s battery would not stay charged. The battery voltage was staying the same, whether the engine was running fast, or not at all. It should go up, from about 12 to 13 volts, when it’s charging.

You can tell from 50 yards away, blindfolded, whether or not a Tomos Revival, Streetmate, Arrow-R charging system is working, by the sound of the horn. When the battery is not being charged, like when the engine is not running, the horn sounds completely smooth. The battery voltage is a steady straight line on an oscilloscope. When the engine is running the the smooth sound becomes more rough. The battery voltage is a straight line with little repeating bumps on an oscilloscope. When you hear the rough sound in the horn, you know that the charging system is working.

The white spot is a reflection from the shiny flat surface of the black insulation, worn from vibration and contact with the stator plate. The fix was to cut away a fingernail size part of the plate.

 

Tomos CDI Ignition

August 13, 2012

Table of Contents

Ignition ……………………………………………………     1

How to test a coil…………………………………….    1

How to check for spark……………………………    1

Ground the coil wire to stop the spark…..    2

Tomos A35 and A55 CDI ignitions…….……..    2

Ignition timing…………………………………………   2

Ignition symptoms………………………………….   3

Ignition

The ignition is like the electric pulses of a heart beat. The voltage pulses are in sync with the rotating crankshaft. When the crankshaft rotates faster (or slower), the spikes are closer together (or farther apart) in time. See figure 5.

Figure 5: Ignition is neither AC nor DC, but instead a train of narrow pulses, each happening at a precise time.

What makes the gasoline ignite is the spark plug sparking, in the right way, at the right time. What makes the spark jump the gap of the spark plug is a sudden very steep rise in voltage, to over 10,000 volts in under a few thousandths of a second. What makes that high voltage spike is a transformer, usually called “the ignition coil”. A transformer is like a car jack. It steps up (or steps down) voltage while stepping down (or stepping up) current. A sudden change in current in the (thicker but fewer) primary windings induces a sudden large change in voltage in the (thinner but many more) secondary windings. Supplying the transformer with a sudden change in current is either a CDI unit (Capacitor Discharge Ignition), on 1994 and later, or a mechanical points and condenser, on 1993 and earlier models. On late model Tomos mopeds with CDI ignition, the electronics are molded into the coil (unlike most Asian types). The “control unit” or “CDI unit” is a small 1.5 inch square circuit board, hidden inside the black plastic of the coil. Early models before 1994 had plain coils, without any electronics.

How to test a coil

Any ignition coil (coil only, not coil-with-CDI like Tomos uses) will produce a spark on a spark plug, at the instant the input wire is touched to a 12 volt battery (+), with the battery (-), coil, and plug all grounded (with clip leads). If you touch it slowly to the battery post, it will produce a weak spark. If you swipe the coil wire fast and hard against the battery post, it will produce a strong spark. This demonstrates that it’s the shorter “rise time”, much faster than the blink of an eye, that makes a better spark. Only perform the above spark test on plain coils. CDI/coils might get damaged from the high current possible. Never connect a 12V battery to a coil for longer than one second. It turns out that moped coils are never bad. Only occasionally the CDI/coils go bad. “Bad” means it produces no spark at all, or it produces weak or intermittent spark. Intermittent spark is like turning a light switch off and on, often in an unpredictable way. The only way to test a CDI/Coil is to put it on a known good running bike and test ride it, listening and feeling for any stumbling or misfiring. If no test bike is available, then the only way to test the CDI/Coil is to replace it with a known good one, and hope that fixes the problem. If it’s not the CDI/Coil, and not the bike’s wiring, then it must be the magneto. The CDI magneto costs way more than the CDI/Coil, and is more difficult to change, and so it’s last.

How to check for spark

CDI solid state ignitions have shorter rise and fall times than mechanical point ignitions. That makes them start with a weaker kick, or even with your hand. CDI ignitions have a faint spark that is sometimes invisible in bright sun. Always check for spark in the shade. “Checking for spark” means removing the spark plug, connecting the plug wire to it, laying it on the engine so that it’s metal shell is touching ground (the head fins), and then turning the engine over (by pedaling backward or kick starting) while watching the gap between the electrodes of the spark plug. Spark color indicates temperature. Blue spark is hotter than pink or yellow. Faint blue spark is good. Bright white spark is bad, usually because of a semi-conductor-coated “fouled” spark plug.  The white porcelain insulator must not be coated with black or shiny carbon. If it is not dull white, tan, or brown, then use a new spark plug to check for spark. A fouled plug will spark badly or not at all, even when the ignition is working fine. You can also hear the snap sound of the spark. Loud is good.

Grounding the coil wire stops the engine 

In both CDI and points type magneto ignitions, the “heart beat” is intentionally stopped when you turn the engine stop switch off. When the “kill” switch is “on” the ignition wire is not grounded. When the kill switch (engine stop) is “off” the ignition wire is grounded. This is the opposite of a (battery ignition) car. So to hot wire a magneto ignition bike you only need to disconnect or cut the kill switch wire so that it cannot be grounded. When troubleshooting a late model Tomos that has bad or no spark, the way to eliminate all the wires in the bike is to plug the black (or red) magneto ignition wire (which has a female blade connector) into the male blade of the coil (or it’s black or red wire with male blade). This isolates the circuit to just the engine and coil. Just remember you can’t turn the engine off.

Tomos A35 and A55 CDI ignitions

There are two types of Tomos CDI magneto ignitions, the A35 type (1994-2006) and the A55 type (2001-later). They consist of two or more coils mounted on a stationary plate, surrounded by a rotating flywheel with four strong magnets molded into it. The A35 ignition has no pulser coil to tell it when to spark. It triggers when the source coil voltage reaches a pre-set level. So changing the location of the source coil (by rotating the stator plate) changes the ignition timing. Tomos provides adjustment slots in the stator plate, and timing marks (thin angled black lines) on the crankcase (minimum and maximum ignition timing), at about the 10 o’clock pposition. An ignition timing strobe light is the only way to check the ignition timing. The strobe light illuminates the fast moving flywheel mark only for an instant. So it appears, magically, to be not moving. The fire mark on the flywheel should lie between the black lines on the case. It should not jump around. The light should not flicker. Once the stator is set in the desired position and the screws are tightened, the timing is set forever, and never needs adjusting (that is assuming the flywheel locating key is in its proper place and the flywheel nut is fully tight). Unlike the A35, the A55 ignition does have a pulser coil that signals the control unit when it’s time to spark. It’s an external pulser (or exciter or trigger) coil that senses a raised strip on the outer edge of the steel flywheel/rotor. So changing the stator position does not change the ignition timing. The A55 external pulser is fixed and mounted in a way that prevents it from being adjusted.

 Left, grinding away the plastic reveals the CDI circuit board and the coil of 233729. 

Figure 6a: A55 “no battery” ignition exploded view       Figure 6b: Same ignition shown in a semi-schematic diagram

         There are about ten different Tomos magnetos for the A35 and A55 engine series. They are all covered in detail in the wiring diagrams collection that this written text supplements. There are also a few more for the earlier A3 models. Before 1986, Tomos A3 mopeds had an external ignition ground that powered the brake light. On those early models if you unplugged the brake light, and then squeezed either brake, the engine would lose spark and cut out. Those early A3’s, with 3-wire magnetos, yellow,  black, and blue, often need the blue magneto wire to be grounded in order to have spark.  After ‘86, all Tomos magnetos are 2-wire magnetos, yellow and black, with no external ground, one less worry.       

Ignition timing

The spark occurs a little before the piston reaches top. That explains ignition timing in one simple sentence. Spark happens before top because the gasoline and air take a tiny bit of time to burn. If the spark happened right at the top of the piston stroke (“top dead center” or TDC), the engine would run, but be weak. If the spark happened twice as early as it should, the engine would run, but be weak and run hot. There’s a preferred range where the “porridge is just right”. Expressed in terms of crankshaft angle, the preferred ignition timing is between 10 and 20 degrees before top. Imagine the flywheel is a pie. Cut the pie in six pieces and you have 60 degree slices. Cut one of those pie slices in three thin slices. That would be a 20 degree angle. That thin slice is a little less than an inch wide on the edge of the flywheel. The time taken for the wheel to move that much is about the time taken for the gas to ignite. At 6000 rpm the piston rises every 0.01 second. Expressed in actual seconds, at 6000 rpm, the spark occurs .01*20/360 = 0.00055 seconds before the piston reaches top. That’s half of a thousandth of a second. You don’t need to know that to fix mopeds, but it makes the lesson interesting and amazing. The faster the engine turns, the less time the fuel has to burn. Because of this, most gasoline engines have variable ignition timing, rather than fixed timing. Four stroke engines like the timing to be about 10 degrees at idle, advancing to about 35-40 degrees at high rpms. They have vacuum advancers, centrifugal advancers, and electronic control units (ECU), to vary the ignition timing automatically. Two stroke engines like the timing to be about 20 degrees at idle, retarding to 10 degrees at high rpms. The explanation is better atomization at higher engine speeds makes smaller fuel droplets which take less time to burn. Before 1994, Tomos A35 mopeds had points, with fixed ignition timing, 20 degrees BTDC. From 1996 on, they had Iskra CDI, with variable ignition timing, 20 deg at idle changing to 10 degrees above about 6000 rpm. The only way to see the timing is with a strobe light made for automobile ignition timing checking. To actually measure the degrees, cars use a thing called a “degree wheel” that attaches to the crankshaft. Any piece of paper with accurate degree lines can be attached to the flywheel, but putting it in the exact correct position is difficult. There’s a clever and simple procedure for finding top. A tool called a piston stop is screwed into the spark plug hole. The crankshaft is rotated by hand until the piston is parked up against the stop. A line is made on the flywheel, adjacent to any chosen case mark. Then the crankshaft is turned by hand the other way until the piston is again parked up against the piston stop. A second line is made on the flywheel adjacent to the case mark. Then a tape measure is laid around part of the flywheel to find the midpoint between the two marks. That is “top dead center”. Fortunately the Tomos flywheels already have inscribed timing marks, one for top, one for fire, spaced 20 degrees apart. The F mark should be between the crankcase marks, when viewed with the strobe. The newer A55 engine mopeds have the same ignition timing but it is not adjustable like the A35 is. That’s Tomos saying don’t mess with a good thing.

Normally, ignition timing is never an issue with CDI ignition 1994-later Tomos mopeds. That is because those magnetos are maintenance free. It is, however, often an issue on the earlier points-ignition models. This is because the ignition timing gets retarded as the points rubbing block wears down. So points need adjustment (spread apart to have more “gap”), and lubing with high melting point grease, every few thousand miles. Besides that, they can be adjusted wrong. The points are designed to open at the right moment in a running engine, when at fully open in a stationary engine they have a gap of .014 to .017 inch (.35 to .45mm). In a magneto with points ignition, the spark happens when the points open, not close. That is essential to know. You can spot check the ignition timing of a points model with nothing but a pen and a flashlight. Find TDC with the pen in the spark plug hole. Rotate backward 20 degrees and see if the points are just starting to open there. In both points-ignition and CDI ignition, the flywheel can be installed in the wrong position on the crankshaft by leaving out the little locating pin. That’s not a normal thing. Neither is running with a loose flywheel nut until the pin shears off and ruins the crankshaft and flywheel. Ouch. It’s also not normal to have some other flywheel, like from a Puch, Sachs, or aftermarket one that has no timing marks or is sparking at the wrong time. A bunch of different moped flywheels will fit the Tomos crankshaft, but they might have the wrong ignition timing because of a different point cam angle. Some stator plates can be installed upside down, making the timing 180 degrees off. Only in these not-normal circumstances you might need to mark the flywheel and check the ignition timing.

 

Tomos A55 Ignition

Here are some pictures of a 2011 Tomos ST magneto.

Above, after 2009, the flywheel says “Kinetic 12V60W”. Rotation is counter clockwise. Since 2010, all models, kick start and electric start, have the outer gear for electric start. That gear blocks the view of the “pulser” or “timing coil”, black at lower right.

Above, a Tomos A35/A55 crankshaft held at the same angle as one in the engine. Roughly speaking, the cylinder is tipped forward to the 10 o’clock position. Here the connecting rod is pointing straight up the cylinder, which is “top dead center (TDC)” or the top of the stroke. When the crankshaft is in the TDC position the crank pin is at 10 o’clock. Then see the little hole in the tapered shaft pointing at you? It is where the flywheel “key” or “roller” or “pin” goes. The flywheel key is at 11 o’clock or 11:30. Right above the crankshaft is the black-wrapped ignition source coil, that’s fixed to the stator. In the upper right corner is the Kinetic pulser, black plastic that’s kind of rough. It is fixed to the crankcase at the 4:30 clock position. This angle, plus the crankshaft key hole angle, plus the angle of the “timing strip” on the flywheel, relative to the key groove (not shown), plus any retard or advance added on by the electronic module or “CDI unit”, is what determines the ignition timing.

Above, two views of the A55 “stator” or stationary part of the magneto. Three clear-coated copper lighting coils are seen at 9 o’clock, 12 o’clock, and 3 o’clock. The 90 degree spacing matches the four magnets inside the flywheel, not shown. The 3 lighting coils are connected in series, grounded internally, and emerge as the yellow lighting wire. Branching off one of the lighting coils is an additional white/red battery charging wire, not shown. At 6′oclock is the black ignition source coil, not connected to the others, emerging as the black ignition wire.  At 4:30 is a black plastic junction box. Also at 4:30, but further out, outside of the flywheel, is a rounded black plastic one inch cube called the “pulser” or “trigger coil”. It tells the CDI control unit when to fire the spark plug, at a precise crankshaft angle. Not shown is the flywheel or external “rotor”, with a raised strip of metal that triggers the spark timing. Notice how the white pulser wire is on the bottom and the black pulser wire is on top. If they are reversed, the ignition timing will be way (like 40 degrees) too early, and the engine will run poorly. The left photo is a 2007 stator, by AET, made in Slovenia. The right photo is a 2011 stator, by Kinetic, made in India. They are both good and interchangeable.

 

Ignition symptoms

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New Tomos Service

August 13, 2012

Welcome to Myrons Mopeds New Tomos Service department.

Here are some articles to help you repair or lovingly maintain your 1992-later Tomos moped. 

Tomos Basics is a mini owners manual, that supplements the regular owners manual.

Tomos Oil Injection is about the simple but difficult operation of installing the left engine cover.

Tomos Throttle Upgrade is about the 1992-07 “throttle valve” sliding block that sometimes breaks.

 

 

 

Tomos Basics

August 13, 2012

Table of Contents

1. Tomos Basics - supplemental owners manual info for new Tomos owners

2. Tomos Revival Battery Installation – there’s a trick to it

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              TOMOS BASICS for USA Models 2007-on (A55 engine)

  1. TOMOS means TOvarna MOtornih koles Sezana (motorbike factory in Sezana, Slovenia).
  2. Warranty is 6 month/4000 mile limited. Owner must send in the warranty registration card located in the owner’s manual to activate the warranty on a brand new Tomos.
  3. Engine is the A55 two-cycle 49cc  single, EPA and CARB compliant with catalytic exhaust. Speed is 30mph. Horsepower is 2hp. Transmission is two-speed fully automatic.
  4. Pedals go forward for hybrid human/motor propulsion. Pedaling speed is 5 to 10 mph. Pedals kick backward for starting engine. Pedal forward to put pedals in kick position.
  5. Gasoline is 90 octane minimum. Only Sprint model is pre-mixed with oil 50:1 or 2.5 ounces per gallon. All other models have oil injection and use straight gasoline.
  6. Gas tank size: LX 1.5gal   Sprint, ST 1gal.  Arrow, Revival, Streetmate .75gal. On the LX and ST locking gas lid, only the key turns, counterclockwise to open.  On ’05-08 Arrow, Revival, Streetmate the gas lid is push in. It pulls straight out. Sometimes it’s tight. After 2008 all gas lids are quarter-turn type.
  7. Gas valve is a manual fuel tap or shut off. It is located above the engine on the left side of the bike. It has three positions, off (horizontal), on (down), up (reserve). Use on during normal operation. Use off when not operating. Use reserve if you “run out of gas”. Reserve lasts 4 to 10 miles. Don’t forget to put it back to “on” after you gas up.
  8. Gas level is checked by opening the gas lid, looking, shaking, and listening. There is no gas gauge. On the LX you can see the whole tank. On the ST and Sprint you can see half way. On the others you can only see the first fourth. Many people choose to install a clear hose branching up from the fuel line. It serves as a gas gauge. The liquid level in the tube is the level in the tank. Gas tank vent: On Arrow/Revival/Streetmate models the gas tank is inside the frame, which is U-shaped. On one end of the “U” is the fill hole, where you add gas. On the other end of the “U” is a vent to let air in and out. It normally lets a tiny amount of air pass but not enough during refueling. When adding gas, the gas tank vent, a black spring-loaded push button, needs to be pushed each time the tank seems full to let any air escape allowing more room for gasoline. It makes a hiss sound. When the ¾ gallon tank seems full and the vent no longer hisses then it’s truly full.
  9. Gas mileage (mpg) is 100 miles per gallon, going 37mph on city streets. If you’re larger, have hills, rough roads, stop and go, your mpg (and range) will be less. If you’re smaller, more aerodynamic, and go slow, your mpg (and range) will be more.
  10. Gas range:  LX 125mi  Sprint, ST 85mi  Arrow, Revival, Streetmate 60mi. Means topped off to hitting reserve, 160lb rider on smooth flat city streets.
  11. Oil is two-cycle oil. It’s slowly consumed by burning along with the gasoline. Use a good brand, preferably synthetic, like Champion weed wacker oil. Without the oil the two-cycle engine will get hot, melt the sides of the piston, and “seize”, with a scary skid.
  12. Oil tank is under the seat, except Sprint, which is premixed in the gas. It doesn’t matter how much oil is in it, only that there always is some. Check the oil level at each gas fill-up. After several gas fill-ups it will need an oil fill-up. 13 ounces lasts about 5 gallons.
  13. Steering lock is on the left front of the frame. To lock, put the steering almost all the way to the right, push the key in while turning it to the right. Move the steering slightly until it finds the hole and goes down 3/8 inch. To unlock, turn the key to the left, pull up, and wiggle the steering if necessary.
  14. Keys: Sprint = steering lock only (2), no ignition key. No battery to turn off.
  15. Keys: ST/LX = steering lock (2) and gas lid (2), no ignition key. No battery to turn off.
  16. Keys: Arrow = steering lock and ignition (2). Turn off ignition and battery after use.
  17. Keys: Revival = steering lock, seat, and ignition (2). Turn off ign & battery after use.
  18. Keys: Streetmate = steering lock, seat, trunk, ignition (2). Turn off ign & bat after use.  Main key switch, also known as “the ignition”, on Revival is on left top of the fake gas tank. On Arrow and Streetmate it’s under the left side of the seat.
  19. Choke is manual. It’s needs to be on (flipped up) for starting when the engine is cold. After a few seconds, when the engine is warmed up, it needs to be off (flipped down). In winter, temp 40 F, the choke is left on for the first two blocks. For normal temp 70 F, the choke is left on for 10 seconds. In hot summer, temp 100 F, it’s not needed at all. Never leave it idling for long periods with the choke on or it will become “flooded”. Never use the choke when the engine is warm or it will become “flooded”. It’s better to under use the choke, than to over use it. If the engine becomes flooded, then it will need no choke and full throttle (maximum air) to compensate for the excess fuel that has accumulated. Running fast cleans it out, and is better for a two-stroke than idling.
  20. Starting:  Turn gas valve to “on”, arrow down. (or “res” if it’s very low on gas)
  21. Starting:  Turn engine stop switch to “run” symbol. It’s on the right handlebar.
  22. Starting:  Revival/Arrow/Streetmate only. Put the key in and turn it on.
  23. Starting:  Cold starting only. Put the choke on by flipping the black lever up.
  24. Starting:  Stand on the ground with the bike on its center stand. Pedal forward until the pedal on your side is in the 2 o’clock position. Have your left hand fingers on the left (rear) hand brake, ready to stop in case it comes off the stand and takes off. Have your right hand on the throttle, with the twist grip turned only just a little, or not at all. Now kick backwards. A broke-in new Tomos starts in one kick.
  25. Starting:  After it starts, rev it up by twisting the throttle. The engine needs to be revved up either stationary on the center stand or moving down the street. Starting it up and then letting it idle to warm up is not necessary or recommended. Its two-stroke crankcase already has the oil film, so it’s ready to ride immediately after starting.
  26. Starting can also be done with the tires on the ground, off the center stand. Pedal the bike forward, maybe 10 or 20 inches, to put one of the pedals in kick position.
  27. Starting can be done while moving. Just stop pedaling and kick backwards.
  28. Electric starting is on Arrow/Revival/Streetmate only. Use the above starting steps, but replace “kick backwards” with “hold the left brake and push the start button”. The start button is where your right thumb is. Then ride for 10 minutes to recharge the battery.
  29. Storage: Ride it with the gas valve turned off, to evacuate the gas from the carburetor. After about a block when it runs out, put the choke on and it will go another block. Doing this will prevent the carburetor from getting coated on the inside with tar from dried up gasoline during storage.
  30. Flooded Starting: Occasionally the moped can become “flooded”, a condition where too much gasoline and not enough air is causing the engine to not start. When this occurs, a different starting procedure must be used. First the gas valve should be turned off. The carburetor holds enough gas to run for at least a minute. Instead of minimum throttle with choke on (up), it needs maximum throttle with choke off (down), to get the most air. Once it fires, it needs the maximum throttle for awhile, maybe 5 or 20 seconds, until the rough running goes away. Then it needs 15-20 minutes of fast running to heat up the exhaust fully, to boil off any unburned gas and oil. During this period it will smoke a lot. If it does not fire within a few full kicks, then the spark plug will need to be removed and the gas or oil dried off it. If the white or brown porcelain insulator is shiny or black, then it will need a new spark plug, NGK BR7ES. Here are the causes of “flooding”. Knowing these before it happens will help prevent the problem.
  31. When a moped is leaned way over, especially with the gas left on, such as when it is being transported, gasoline can spill into the air filter or into the intake port of the engine, and result in not starting. This also can happen on Revival and Streetmate when gasoline spills over during filling. When the engine is run with the choke on too long, the spark plug can get wet with too much gasoline, and result in the engine not starting. Idling for too long, or going slow all the time can also cause this. When the engine is kicked over many times without having a spark, such as when the kill switch is left in the off position, the spark plug can get wet with gas and result in not starting.
  32. If the float valve inside the carburetor malfunctions, gasoline can spill into the air filter. A tiny fiber can cause that, or tar from a long time sitting, or a worn needle valve and/or seat. If the oil injector leaks oil into the engine during storage, then the spark plug can get wet with oil. Remove the spark plug, kick over the engine to push out any excess oil, and clean the oil off the plug.

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Tomos Revival Battery Installation

Left, two views of the Revival battery. It’s a common size used on most modern 49cc bikes with electric start. It’s a 12 volt 4 amp-hour, gel cell sealed type, BTX4L-BS or compatible. It has to lay sideways and the rear terminal wire has to be like shown, or else the cover won’t close all the way. Even when it is correct the cover has to be pushed tight to make the screw holes line up. 

Tomos Oil Injection

August 13, 2012

Tomos Oil Injection and Left Engine Cover Service

2011 Tomos ST with left cover removed.

Tomos has made oil injected mopeds, US models, for over 33 years, since the 1979 Silver Bullet. Ever since, every deluxe Tomos with oil injection has a small oil pump mounted onto the left engine cover, over the magneto. They have an excellent reputation. The highest mileage mopeds, in general, are the oil injected ones. When the engine is not too modified, the oil injection gives it the right amount of oil, automatically, all the time. You don’t have to mix the two cycle oil with your gasoline if you have oil injection. Serious commuters and most people in general prefer the convenience of oil injection and are willing to pay a little extra for it.

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Above, close up of 2011 ST flywheel. At center, the special nut with a groove in it for the oil injection pump. Until about the mid 2000′s, the magneto nut had two outer prongs that held an free floating aluminum disk with a groove in it. This upgraded nut has a steel disk rubber mounted and bonded to the nut. Click to enlarge any of these pictures.

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Inside view of left engine cover showing oil pump tongue.

The left cover is easy to remove, but hard to put back. The tongue on the oil pump must be pointed in the same direction as the groove in the flywheel nut. Besides that, two precision 9.8mm sleeves, one at the upper cover bolt, and one at the lower cover bolt, must line up with their holes in the aluminum engine case. What is difficult is you can’t see it. It’s a “blind operation”, which is something that is done with your eyes closed, mostly by feel. When you think the tongue and groove are at the same clock position, say 12 o’clock, then you must turn the cover around and place it exactly on the two alignment sleeves. It usually never goes all the way on until you hit it lightly with the soft side of your fist. When it’s not lined up, it makes a thud or thump, and there is still a small, like 1/16 inch gap between the cover and the case. When it is lined up, hitting it lightly makes a loud clap, as the aluminum cover slaps or snaps together with the aluminum engine case.

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On this flywheel nut, the oil pump groove is completely rounded. It no longer drives the pump.

As long as the person doing the service does the procedure properly (lining up the tongue and groove) and does not leave out the alignment sleeves, the oil injection performs reliably for many tens of thousands of miles. The most common source of trouble is improper servicing. When the tongue and groove are not engaged, there is a small 1/6″ gap between the cover and the case. If the three cover bolts are then installed and tightened down, the cover will be forced to go all the way on. Eventually the oil injection will fail when the groove hole becomes completely rounded out, and no longer engages the tongue. When that happens, the oil pump stops pumping, and soon after that the engine seizes up.

Tomos Oil Line Clamps and Oil Tank Repair

Tomos oil line clamps work good when they are put on right. Here’s all about it.

Left, factory installed clamp. Middle, spreading with a dental tool. Right, lifted over the lip of the spigot. You can see a green “tail” on the right of the cup. What’s funny is that is not the crack, but it looks like one. Slightly pressurizing the tank with air revealed that there was a crack, as oil was seen leaking out. The real crack is where the punch is in the middle picture. Nothing sticks to this kind of plastic, so plastic welding or tank replacement were the two options.

 

Left to right: 1) Spreading open the crack with a tapered punch. Then cleaning off the oil with spray solvent and compressed air. Then warming the plastic with a soldering iron, pushing softened plastic from either side towards the crack, filling the center. Then pulling the punch out to allow the tension to close the crack. After cooling the sealing surface around the hole is made flat with a disc grinder. 2) The plastic welded oil tank, ready to put back on. 3) An old pliers is ground away about 1/16″ from the end, to make an empty pocket for the loop part of the Tomos oil line clamp. 4) Squeezing the clamp tight with the special pliers. 5) The oil line is re-clamped properly. You cannot rotate the oil line or clamp, because it is tight. The loop of the clamp is not smashed, thanks to the cut away in the pliers.Click on the far right picture and you’ll see the rounded loop. When the loop is smashed, it can eventually break and come off. That can be a mess, or it can be a disaster.

Final Bleeding of the Short Oil Line

After the oil is put back in, the long oil line, which supplies the oil pump is bled by removing the bleed screw. Once that is done, only the short line from the pump to the engine is still full of air. The only way to “bleed” that is to run the engine on temporary gas with oil mixed in. It takes 5 or 10 minutes to go about 10 inches. The oil flows very slowly, about 3-4 drops per minute, at 7000 rpm.

 

Tomos Throttle Upgrade

August 13, 2012

Tomos 1991-2007 Throttle Upgrade

This is about how to repair an A35 throttle that has a bad “throttle valve”, in case the original part is not available.

Above, the bottom view of the throttle used on all A35 (except A35 Revival) and A55 models from 1992 to early 2008. Everything is black except the light grey “throttle valve”, also known as “sliding block”. It is Tomos part number 223707. Since mid 2008 the controls are different. They say TBS, and the throttle is a wrap-around type, so it has no sliding block.

Above, the same throttle with a pinch bolt upgrade. When the sliding block breaks or strips and cannot hold onto the cable wire, a throttle pinch bolt, 5mm diameter by 7mm long is installed on a new throttle wire just behind the broken sliding block. First a new throttle wire is installed and lubed. The old sliding block must be in otherwise good condition, other than it cannot hold onto the wire. A 5mm diameter by 7mm long throttle pinch bolt is slid over the end of the new throttle wire, and positioned against the sliding block. The wire is pulled taut. The screw is tightened with a small sharp proper fitting screwdriver, very tight. With the engine not running, the throttle is operated to see if it works and feels right. Then the excess wire is cut off, with a sharp wire cutters (diagonals), when the throttle is held at max, engine off. The short tail should be about 1/4″, like shown above. Bend the tail if it hits the grip at max position.

Above left, exploded view. Middle, broken 223707 with pinch bolt back up. Right, pinch bolt 5mm diameter x 7mm.

Warning. Improper installation or using a bigger or different pinch bolt might make the throttle stick or stay on. Many other things can also make the throttle stick, such as lack of lubrication, or a kinked or frayed cable. See Service/Carburetor for info about sticking throttles. Do not let anyone operate the moped if the throttle is sticking. It should always snap back to idle when you let go. This information is for service personnel and competent home mechanics, not just anyone. Please get help if you need it. Use discretion, and use this info at your own risk. The author assumes no responsibility for the use of this information.

Tomos A55 Transmission Oil Leak

August 12, 2012

Occasionally new mopeds, 2008 and later, leak transmission oil (ATF) at the front chain sprocket. The chain then slings the oil onto the rear of the bike. Here’s why.

With the distance bush removed you can see the thin o-ring #31 (033007). The white surface around it is the inner race of the big ball bearing #22. Click to enlarge images.

 

 

Sealing the coaxial drive is tricky. Oil can leak from three concentric circles.

  • 1. the circle between the central pedal shaft and the drive shaft #23
  • 2. the circle between the drive shaft #23 and the distance bush #20
  • 3. the circle between the distance bush #20 and the outer big seal #21.

1. Leaks from inside the drive shaft

Pressed deep into the center of the coaxial driveshaft #23 (223453) is needle bearing #24 (033502). It’s left end has a thin rubber seal. This generally does not leak except in some high mileage machines, or if it is damaged during installation of the pedal shaft by a sharp corner at the end of the pedal shaft, such as caused by crashing or abuse. Tomos intentionally rounds the left end of the kick starter/pedal shaft, so it can’t cut the seal as goes in. When this “inner” seal leaks, the whole engine must be completely disassembled, to replace the driveshaft #23 (223453 for pedal, 223456 for kick), complete, at a cost of about $150 parts and $250 labor. Total $400. This is Option 1A, the way Tomos says in the 1985 A3 Service Manual, “In case of damage to the needle bearings in the main shaft, we suggest it’s replacement with a new complete main shaft.”

Alternatively, the motor can remain installed and assembled, except for the transmission gears and shafts, which are removed from the right side. Then it is possible to remove the leaking left needle bearing from the drive shaft on the right side. A very special custom modified inner jaw slide hammer type bearing puller tool is necessary. Then the cost, in most small shops, is about $220 for making the tool, plus $150 labor, plus $30 parts. Total $400. This is Option 1B, for skilled toolmakers. It is not in any Tomos service manual. But Tomos does sell the parts to do it. 

Left, Tomos says in the 1992 A35 Service Manual, in case of damage to the inner main (drive) shaft seal or needle bearings, to remove them using a suitable tool, and install new ones with press tool 732.367. 

Right, the installer 732.367 with a 16mm to 20mm step. The extractor 706.485 and extractor bridge 706.472 are for extracting the 12mm ID left counter shaft bearing, and the 12mm wheel bearings. Apparently, Tomos does not say how to extract the 8mm and 10mm ID transmission cover bearings, and the 16mm ID drive shaft needle bearings, in any of their manuals.

Much skill and craftsmanship is required to select, make or reshape the tool. Otherwise it tears up the delicate needle bearing, leaving the thin shell stuck in the bottom of a deep hole. That mess takes hours to clean up. The bearings are painstakingly peeled off in small pieces, like peeling a stubborn steel orange that’s down in a tight hole. You can barely reach it and see it. But you save $100.

Left, a Tomos drive shaft 223453 showing the two needle bearings installed. The kick driveshaft 223456 is identical except it is smooth and flat where the ring of ramps is. This particular one has broken all of it’s ramps off. The deepest bearing 033502 has a rubber seal at the left (deepest) end. Above it is 033503, another needle bearing, not as wide and without any rubber seal.

Right, the puller in action. Below right, the bearings are out, but still on the puller.

 

 

Left, the two jaws must fit the 2o.5mm OD yet pass through the 16mm ID.  Wider jaw lips and more jaws would be better.

 

Left, the left sides of needle bearings 033502 and 033503. Right, the right sides.

 

033502 says “SNL  SCE109RS” and 033503 says “SNL  SCE108″. You can see the damage the puller did. You can see the black rubber seal on 033502, near the puller damage. When oil leaks from the center of the hollow coaxial drive shaft, rather than from under the surrounding distance tube 209077, it is from this seal, deep deep inside.

Right, the empty drive shaft with it’s bearings out, plus a thick rubber o-ring #30 (033006). The o-ring is an upgrade that comes on the newest bikes, 2012 and 2013. It is a heavy duty back up to the little seal in the left needle bearing. Left to right, the o-ring goes in the hole first, then the bearing 033502, seal side down, then the bearing 033503. These things are super easy to put in, just press straight in, with precise hammer taps. But they are super difficult to get out, even for professional mechanics.

 These two ways of fixing the inner leak, Option 1A and 1B, are very difficult and/or very costly. They are the options that use Tomos original parts.  

  

 

A better way is with a special sprocket nut, custom made by Myrons Mopeds, with a built-in seal. This is Option 1C. See Showcase/Showcase for the price and more info. At left, the upgrade nut, uses a 32mm wrench, precision machined to accept an off-the-shelf 16 x 24 x 6 metric oil seal. At right, an original Tomos front sprocket nut, M22 x 1.0, uses a 30mm wrench. This is only for when the back side of the sprocket is bone dry, and the pedal shaft is dripping wet where it exits the drive shaft, which means the leak is from circle 1, inside the drive shaft only.

 

 

2. Leaks from outside of the drive shaft

Before 2008: metal to metal in three places

2A. The back side of #20 distance bush 209277 against the front side of the #22 bearing.

2B. The front side of #20 distance bush 209277 against the back side of sprocket #17.

2C. The front side of sprocket #17 against the nut #19 and washer #18.

After 2007: o-ring upgrade, no more metal to metal

2. The beveled surface of distance bush 209077, against o-ring 033007, against #22 bearing.

Before 2008, a scratch on any one of those metal surfaces would cause a leak. But that almost never happened. The parts were always made precise and smooth. What’s funny is that the oil seal #21 rarely or never leaks. Until ’07, only a loose sprocket nut caused a leak. The sprocket and distance bush were almays made flat and never leaked. In 2007 we started seeing wavey sprockets. Dished sprockets on Revival, Streetmate, Arrow had their washer tab hole too far in towards the center. Myrons used to weld part of that and grind flat. Flat 26T sprockets 209078 were made warped by the stamping. Also in 2008 many distance bushs had deep gouges in them.

Tomos upgraded the 209077 distance bush by wedging an o-ring in the corner of driveshaft #23, bearing #22, and the back side of #20, and cut a bevel (about 30 degree angle) cut on the inside back corner of #20, to compress the O-ring as the sprocket nut is tightened. Then the wavey sprockets didn’t matter, since the O-ring stops the oil from reaching the sprocket in the first place. Even though they had the right idea, there were several problems with the 2008-2009 O-ring-sealed distance bushes 209277. Some were installed beveled side out instead of in. Some were made without enough bevel, also cutting the O-ring #033007. The dark colored distance bushes, made in India, in the current (2009) parts inventory are made right. Their bevel is 2.6mm wide. At least some of the ones coming on the 2009-later bikes are made with only a 2.0mm wide bevel, which somtimes pinches the o-ring during installation.

At left is an actual distance bush. It’s made of tool steel. It’s from the current (Aug 2012) Tomos USA inventory. It’s well made and correct. OD=34.75 ID=30.40 H=10.92mm

 

 

 

Right, 3 distance bushes, L to R, cut too much – won’t squeeze o-ring, cut just right, cut not enough – can pinch o-ring.

 

Even with a new o-ring and distance bush, oil still can leak here. Once the o-ring is seated and everything is clean, a liquid gasket such as Three Bond can be applied to the inside of the distance bush. Then the distance bush is put in place carefully, trying to squeeze but not pinch the o-ring. More liquid gasket can be applied to the back of the sprocket. Then the sprocket is put in place. Some more liquid gasket can be applied to the center splines and and front side of the sprocket. Then the tab washer and 22×1 nut is installed and tightened, with liquid gasket on the threads. That tends to be the final answer. 

 3. Leaks from outside of the distance bush

 3. The inner lip of #21 (036620) oil seal, against the rotating outer surface of #20 distance bush 209277. This almost never leaks. The big seal, 036630, size 35 x 47 x 7mm, that you can see, seems to be the obvious guess. That guess is, 9 times out of 10, wrong. Replacing the big outer seal usually does not stop the oil leak (unless the seal was attacked by a screwdriver).

 

Horizontal Cross Section View of Driveshaft Assembly

Colors:  Pink = Transmission Fluid     Green = aluminum case         Note: the upgrade o-ring #30 is not shown

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