Tomos Basics

August 13, 2008

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, 2008

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.

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.

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, 2008

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, 2008

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. MM made and sold these from 2003 to 2010, but no more.

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

Tomos Balanced Clutch Drum

August 12, 2008

The Tomos two-speed automatic dual clutch drum, located behind the bulge in the right side of the transmission cover, is about 4 inches in diameter and made of two stamped sheet steel drums crimped onto a center tool steel precision shaft with gear. In the picture below, the view is of the outboard side, which is the first speed centrifugal clutch side. Flip it over and you would see an identical drum, facing opposite, with a small 1 inch straight-cut gear, the “first speed driving gear”, attached to the inboard side of the dual clutch drum, which is the second speed centrifugal clutch drum.

These drums can be made slightly out of round. They are machined on the inner surface only, where the clutch shoes slip and grab, according to speed. That machining is always perfect, as the inside surface is perfectly concentric with the one-way needle bearing. The proof is there is never any rapid pulsation during clutch slip. So the drum and clutches function perfectly. When the outer surfaces are out of round, the whole bike vibrates or buzzes, and gets worse when the engine is revved up going fast. That buzzing can be felt most in the hands and feet. It can make the mirrors blurry. It can make the speedometer go wild. It can make things on the bike crack, break off, or come loose.

When the drum is a little off balance, and the set of three clutch shoes is also a little off balance, then the vibration felt in the bike can become worse at times, more or less at random. This is because every time the bike slows down, the centrifugal clutches let go of the drum as the spring pulls them inward, and they begin to rotate inside the drum. Then when the bike speeds back up the clutches fly out and grab the drum, because of centrifugal force. But they end up in a new random location in the drum. If the heavy side of the clutch is opposite the heavy side of the drum, then there will be minimum vibration. If both heavy sides are together, there will be the most imbalance and the maximum vibration felt.

Other things can cause excessive engine vibration. Installing a heavier or bigger piston, like a 65cc, is the most common. Running with a loose flywheel or clutch nut is one. The magneto flywheels all seem to be balanced good, although they have not been tested. Using mis-matched clutch shoes is another. Not only should they all weigh the same, but they should all be equal in wear, not one new and two worn out, for example.

Above, the Tomos clutch drum. This one is extremely out of round, so bad you can see it with your eyes. Look at the thick wall on the left. Now compare that with the thin wall on the right side. Clearly the left side is heavier! When they’re bad they’re usually less than half this much. The out of balance clutches began around 2008. Before that, from 1976 to 2007 there was never any noticeable balancing or vibration problem. The A35 (1991-2006) and A55 (2002-later) have the same clutch drum. The A3 (1976-1990) one looks the same but parts of it are smaller or thinner.

Pressed into the center of the clutch drum is a precision roller clutch, a needle bearing that only turns one way. In the picture below, the roller clutch is installed correctly, with the plain side facing out, and the writing side facing inward. When you rotate an installed Tomos clutch drum clockwise, it engages the crankshaft. When you rotate it counter-clockwise, it spins free. When a Tomos engine seizes or hydraulics (that’s when the piston slams into incompressible liquid – gas or oil), the roller clutch can become damaged. It usually becomes tight or frozen. When a Tomos roller clutch is frozen, the bike will run fine but won’t go into neutral when you slow down to stop.

How to “balance” the drum:

A machine shop or a home machinist with a lathe, can perform a precision cutting operation. The drum is held by it’s inner surface, and turned in a lathe. The high parts of the outer surface are “skimmed off”. Try to leave the lowest part uncut, to give it the most strength.

 

Tomos Stripped Driveshaft

August 12, 2008

On pedal models only, not kick models, during the years 2008-2009, occasionally a driveshaft 223453 would become stripped at the ring of ramps needed for forward pedalling. This can never happen on kick models, because they do not have a ring of ramps. When the ring of ramps becomes stripped, the bike runs fine and kick starts backward fine, but the pedals just spin free going forward and do not propel the bike forward at all.

Left is a 223453 driveshaft brand new. Right is a 223453 stripped at the ring of ramps. No ped, only mo!

Some people live with it like that because it’s expensive to repair. The cast iron chips need to be flushed out, or else one chip can damage any one or even all of the gears. It’s too big a gamble to leave them laying in the bottom back corners of the transmission compartment. If the bike is ever leaned way over, the little iron chunks and bottom oil sludge will be poured over the gears.

More to follow…

 

Tomos A55 Derestriction

August 11, 2008

1. Removing intake air flow restrictor

This is the 2010-later carb, with red silicone over idle mixture screw. The PHVA14 has an idle speed screw, with a big knob sticking out for the rider to use occasionally, and a idle mixture screw, recessed with a slot head, for the service technician to use.

The “elephant trunk” restrictor is exposed, a hidden part of the junction sleeve 233748 that joins the air filter/silencer to the carburetor.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This is after the rough cut.

This is after smoothing and rounding with a rotary file.

 

 

 

 

 

 

 

 

 

 

 

 

2. Replacing the rear sprocket

Sprint, ST and LX models come with 28 tooth. Replace that with 22 tooth and subtract 3 chain links.

Revival and Streetmate models come with 31 tooth. Replace that with 24 tooth and subtract 4 links.

 

 

 

3. Shortening the stock exhaust

Only welders and metal workers can do this. But the benefits are huge. Speed increase from 37 to 43 mph.

 

 

 

 

 

 

 

 

 

 

 

 

Encarwi Service

May 4, 2008

Encarwi Carb Service for Tomos A3 1974-83

This very simple, early Tomos carb is designed to be serviced without removal. After 1985, Tomos A3 & A35 models came with Dellorto SHA14/12 carburetors. The Tomos A3 carburetor is in a confined area above the engine and below the sheet metal gas tank/frame. It is difficult to remove.

 Two super usfeul and easy checks:

1) Check the jet. With a large flat head screwdriver or a 9mm wrench, remove the jet holder #2. Remove the jet #2 with a medium-thin flat head screwdriver. Hold the jet up to a light source, such as a sunny white wall. Look through the tiny hole to see if light gets through. If it’s pitch black it’s completely blocked. If it’s not circular then it’s partially blocked, like by a fiber.

2) Check everything else. When the jet holder is removed, and the gas valve is turned on, gasoline should flow out of the gas tank, through the banjo bolt #16 at the float top #12, and then dribble out the hole where the jet holder was. This is a way to quickly test the fuel system, tank, valve, line, filter, and float, all at once.

If gas does not spill out with the jet holder removed, then gas is not getting to the jet. Check if gas comes out of the tank. If gas is getting to the carburetor, but not getting to the jet, then either the inlet banjo #14 or banjo bolt #16 is clogged, or the float top #12 is clogged, or the float #11 is in upside down, or the float is stuck in the up position. Several things can cause this kind of float to stay up and not drop down and let gas come into the float bowl reservoir: being installed upside down (pointy end goes up), rust powder filling up the guide hole at the bottom of the float chamber, the float bulb being pushed too far down the rod, the wrong float, or a dented float chamber wall.

 

Servicing

The jet holder #4 unscrews from the left side. It holds the jet #3, Bing 3.5mm size 46.

To remove an old, hard, shrunken and very stuck on, fuel hose, be careful not to break off the “neck of the banjo”. That means you only pull straight out and rotate, never pull or twist sideways. If that fails, a diagonal pliers aka dikes aka wire cutters, can be used to cut the old fuel line, parallel to the hose, without cutting the banjo underneath. The cut does not need to go all the way through the old fuel hose, but far enough to weaken it.   

To service the float, loosen the clamp screw #20 and rotate the carb so it is tipped to the right. Remove the 11mm hex head banjo bolt. Remove the two slot head screws #18. Lift off the float top. Lift out the float with your fingers. It should lift out freely and not feel stuck.

Float versions, left 70’s bulb, right 90’s solid

 

 

 

Things that cause not enough gas:

Rust powder filling up the guide hole at the bottom of the float chamber. Remedy is twisting a correct size drill bit with your fingers, to pull the powder up and out of the hole. With the jet holder removed and the gas valve turned on, gasoline should flow out of the tank, through the float valve, and spill out the jet holder hole. The amount should be enough to fill the float reservoir in a few seconds, which is roughly a spoonful every 4 seconds.

The bulb being pushed too far down the rod. Remedy is to push it back up. See the above photo with measurements.

Dented float chamber wall. Remedy is to grind or sand down the high spot.

Blocked float reservoir air vent. Gasoline cannot come in unless air can get out. Remedy is to find where it is blocked at, and remove the blockage. The vent follows a channel in the back mounting surface. An empty float reservoir should fill up in a few seconds after the gas valve is turned on. To test for a blocked air vent, first empty the reservoir, then turn the gas valve on for 8 seconds and then off. Then remove the jet holder, allowing gas to dribble out, to see how much gasoline there was in the reservoir.

Blocked gas tank air vent. Gasoline cannot leave the gas tank unless air comes in. So there is a pin hole in the gas cap. When the tank is full, and the vent hole is blocked, the bike will seem to run out of gas. To test for a blocked gas cap vent hole, first fill the gas tank, then close the gas valve, then remove the fuel hose. Place a clean container under it (to check for purity and to put the gas back in the tank). Turn on the gas and observe the flow. It will flow normal at first. But in a few seconds, as negative pressure builds up, the flow will slow down and stop, if the vent is blocked. If the flow continues for 20-30 seconds (or indefinitely) then the gas tank is vented.

Things that cause too much gas:

Worn float needle tip. Remedy is to sharpen it. Examine the tip with a magnifier. Spin the float with a drill while pressing the tip gently against a sheet of emery cloth or very fine sandpaper, at the same angle, and move it slowly around to fresh parts of the sandpaper. The needle rod must be straight first. Examine the tip with a magnifier. There should be, everywhere on the cone tip, circular sanding marks, and no more circular “potholes”.

The needle is bent. Remedy is to straighten it. Normally the bend is just above the top of the bulb. It is done with just fingers and eyes. Rotate to see which way it needs to go. Bend a little. Repeat. 

The bulb being pushed too far up the rod. Remedy is to push it back down. See the above photo with measurements.

Worn float seat hole. The float valve seat is part of the float top. It is the tiny hole at the bottom of the small hole. Examine the hole with a magnifier. It should be perfectly circular and free of nicks and scratches. Polish it with a spinning tooth pick, or the stalk of a Q-tip. 

Float bulb has gasoline inside it. If the float too heavy, it won’t have enough buoyancy to stop the gasoline from getting in. Remedy is to evacuate the fuel with compressed air, locate the leak hole, and apply a minimal amount of fuel tank sealant. 

 

Servicing the M56 engine’s H12 or H8 Carburetor:

One problem unique to this carb is warping of the engine side surface. This is caused by over tightening the two mount bolts, and maybe also because the heat block behind it is semi-soft. The back side must seal not just air, for good idling, but also there is a fuel passage that can leak because of a warped carburetor body. The remedy is to grind the back side flat again, without taking too much off. In the body, there is a narrow fuel hole at the bottom of another hole, that is impossible to see directly. That hole must be checked and cleaned with carb spray and compressed air. 

The float is the same as the other carbs. The float top is the same except it has no air vent pin hole. The idea was to not let gas spill out the vent hole. Instead the vent goes to the mounting gasket, where there is a small opening to the atmosphere, higher up.

 

 

 

Bing Carburetor Service

May 3, 2008

Bing VergaserContents:

1. Carb Elbows: Long and Short

2. Exploded View and Parts Names

3. Carburetor Service Info Sheet

4. Float Needles: Rubber tip and Metal tip

4. Floats

6. Fuel Mixture is Controlled by Five Things

 

1. Carb Elbows Long and Short

Sachs Bings can have long or short cable elbows.

Puch Bings can have long or short cable elbows.

 

 

 

 

 

 

 

 

 

 

Sachs Bing Cable Elbows: Left photo above, left is the long carb elbow, used on KTM Foxi, Sparta Buddy, and most Sparta Foxi models. Right, is the short carb elbow used on other Sachs engine models. The Sachs elbows are 7mm, not 6mm threads like Puch ones. The bigger elbow allows the throttle cable small end to pass through the 6mm adjuster. So Sachs double-ended throttle cables do not come with adjusters. The adjuster stays with the elbow. Puch Bings have 6mm elbow threads, and 5mm adjuster threads, too small for the cable end to pass through. So Puch double ended throttle cables have the 5mm adjuster trapped in them.    

Puch Bing Cable Elbows: Right photo above, left is the long carb elbow, used on Maxi models, also with the black choke extension. Right, is the short carb elbow used on Magnum type models. The current aftermarket “Puch” throttle cables are made for the short carb elbow. They idle way fast if used with the long elbow, because the slide is not allowed to go fully down to idle. Myrons sells a long elbow throttle cable, for Puch Maxi, made from a modified “Puch” throttle cable. The wire needs to be about 12mm longer. The long elbow comes on Maxi type sheet metal frame models. The short elbow comes on Magnum type tube frames, such as Sears Free Spirit or JC Penney Pinto. The short elbow is so your foot does not hit it when you get on and off the bike. See the exploded view diagram below. Other Bing moped (under 15mm venturi) carburetors are the Sachs Bing, Kreidler Bing, Solo Bing, Tomos Encarwi, Batavus Encarwi, Trac Encarwi. Much bigger Bing carburetors are also on BMW, KTM, Penton, Sachs, Maico, DKW motorcycles, all made in or near Germany.

 

2. Exploded View and Parts Names

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3. Carburetor Service Info Sheet

Below, the choke slide and throttle slide must be installed simultaneously. It is difficult. The throttle slide has a slot that must line up with a prong in the carb body. The top of the choke slide slides onto a deep wide notch at the bottom of the choke rod, so moving the choke rod moves the choke slide. It often gets left out or disconnected. When the choke slide is disconnected from the choke rod, the choke will be “on”, blocking off the air supply, whenever the throttle slide is down or closed. Normally when a Puch is given full throttle, the choke slide and rod are lifted all the way up until it clicks. The click is the choke rod clip #24 settling into the clip groove near the middle of the choke rod #23. When the throttle cable is not adjusted tight enough, the choke is not lifted all the way off, and it does not click until you manually reach down and pull up on the choke rod. When the throttle cable is adjusted too tight, the engine races and does not idle slow, even with the idle screw loosened all the way. See also General Carburetor Service and Jetting for how to clean and adjust carbs in general. 

 

White Flakes

These white flakes were the cause of a customer’s Puch not running. By chance a tiny spec broke off and lodged in the main jet.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4. Bing Float Needles 

All “Bing Puch Carbs” have the slotted float type float needle with a rubber cone tip, except for some of the Sears Free Spirit 1/14/163  and 1/14/164 carbs, which have a Sachs Bing type float needle that does not lock into a slot in the float and has a metal cone tip.

 

5. Floats

The original 1970’s floats were white. They weigh 5.6 grams when new. Modern replacements are black. They also weight 5.6 grams. 

After years of exposure, the original white floats gradually absorb ingredients from the fuel and oil. They turn color, first light gold, then gold, then orange-gold, then light brown. The darker the color the more wight they gain, and the less they float.  Orange-gold used floats weigh 5.8 g, light brown ones weigh 5.9, brown ones weigh 6.0 g.

 

6. What part controls mixture depends on how much throttle opening

Slide Carburetors Diagram

 

 

 

 

Ignition and Magneto Service

April 20, 2008

Welcome to Ignition and Magneto Info for 1970s and 1980s mopeds, USA models with brake lights.

Contents:   1 Magnetos    2 Magneto-Points Ignitions

Contents:   3. Clip-on Condenser   4. Magneto Wires Chart 

Contents:   5. Hot Wiring     

 

1. Magnetos

Moped magnetos have two parts, a rotating flywheel/rotor, and a stationary stator.

They have two functions, producing the source of ignition spark, and generating power for lights.

Most magnetos worldwide have two functions that are independent and unrelated. The lights function independently of the ignition, and the ignition functions independently of the lights.

The fact that the headlight comes on when the engine is turned over does not mean that the spark is good or bad, because head lights (except Angel/Speed Bird and Motobecane) are separate from ignition.

 

 

The best resource for moped electrical is Moped Army Wiki. www.mopedarmy.com/wiki/Electrical

Tomos A3 Stator

Typical Stator Assembly: At left is an original 1974-1986 Tomos A3 stator, the stationary part of the magneto. Left is the points, right is the condenser, top is the ignition source coil (with two output wires, black and blue), bottom is the lighting source coil, with one output wire, yellow, at top right (not the yellow from condenser to points). The ignition source coil has an external ground (the blue wire), while the lighting coil has an internal ground (the solder joint at lower right).

 

 

 

 

 

 

 

 

2. Magneto-Points Ignitions

 

 

 

Below is another Myrons hand-out sheet explaining internal and external ground ignition circuits.

 

3. Clip-on Condenser

How to tell if the condenser is bad:

This is a very useful troubleshooting technique. A condenser can be added temporarily without removing any parts. At left is a “Clip On Condenser” a valuable tool. When a running bike is having ignition misfires due to a bad condenser, this external condenser will reduce or stop the misfiring or “hiccuping”. It can be any older automobile condenser. It can be located anywhere along the wire that runs from the points, inside the magneto, to the spark coil outside the engine. It only takes a few seconds to “T” the condenser off the coil wire, clip the ground somewhere, and go riding.

 

External condenser diagram

 

 

 

 

 

 

 

 

 

4. Magneto Wires Chart

Myrons Magneto Wires: what the wires do and which are needed to run

Myrons Magneto Wires: what each wire does, and which are needed to run

 

The Magneto Wires Chart above is like a master key that unlocks a lot of different mopeds. Knowing the color and function of the magneto wires allows a moped engine to be “hot-wired” to run without any of the bikes wires.

 

5. Hot Wiring

“Hot wiring” is the same as making an engine run, say on a work bench, completely separate and disconnected from the bike. Certain magneto wires matter, and must go to certain places. Other magneto wires are for lights only. The ignition wire must always go from the magneto (points, condenser, and source coil) to the spark coil, and not also to ground. The ignition ground wire must always go from the magneto (source coil ground) to ground. You can make this happen easiest with alligator clips on the ends of wires, like little jumper cables, called clip leads.

 

To make any moped motor run on a work bench, you need some clip leads, a spark coil, a good spark plug, and the knowledge of what each magneto wire does. For example, on most Puchs, blue is ignition, and blue/black is ignition ground. On a Garelli, black is ignition and blue is ignition ground. On a Derbi, green is ignition and blue is ignition ground. Sometimes the wire colors are faded to grey, dark brown, or black. Then slice some skin off with a sharp knife to expose the true color inside.

 

 

6. Extending a Copper Core Spark Plug Wire

 

 

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