Keihin Carburetors

January 3, 2015

Contents  1. Keihin (early PC50)    2. Keihin (PC50)    3. Keihin (Indian)    4. Keihin (PA50)

                 5. Keihin (1977-79 NC50/NA50)     6. Keihin (1980 NC50/NA50)    7. Keihin (1981 NC50/NA50)

                 8. Keihin (81-82 NX50, 82-83 NC50/NU50)     9. Keihin (1983-85 NQ50/NM50)

KeihinWelcome. Keihin carburetors are used on almost all Honda motorcycles (or copies of Hondas). Here we focus on the 50cc moped and scooter carburetors from the 1970’s and 1980’s. First is an indroduction from Wikipedia

The Keihin Corporation was founded December 19, 1956 and currently maintains its head office in Shinjuku Ward, Tokyo, Japan. Among the products they are internationally known for is the production of carburetors and fuel injection, and is a major suppler to Honda, and also Triumph, Suzuki, Kawasaki, KTM and Harley Davidson motorcycles. In addition to carburetors, Keihin supplies the automotive industry with engine, transmission and climate control products, including intake manifold assemblies, HVAC assemblies, compressors, valves, solenoids and electronic control units. Keihin’s largest shareholder is Honda Motor Co. Ltd. Keihin first began U.S. manufacturing in 1989. Counting all U.S. locations, Keihin has more than 20,000 employees. Keihin North America’s corporate headquarters is in Anderson, Indiana.

E-clips for jet needles

E-clips for jet needles

Keihin motorcycle carburetors are labeled with a cast-in model code followed by several numbers and letters that specify the settings for that application. Except for the Honda PA50 carburetor, which is a unique design, these moped and scooter carbs are all model code “PA”. Other Keihin carburetor model codes are PC, PD, PJ, PWK, CV, CVK, VB, VD, VE.

Keihin PA series: First up are parts that are the same on other Keihin PA series carburetors, like screws, jet needles, jet needle clips, jets, o-rings, float needles. More will follow… 

 

 


1. Keihin C5A (early PC50) 1968-72 Honda PC50 Little Honda

1969 Honda PC50 carburetor illustration

1969-70 Honda PC50 (USA)

1969-70 Honda PC50 (USA)

 

 

 

 

 

 

Honda early PC50 carburetor

Keihin C5A carburetor, spigot mount.

Honda PC50 float bowl missing the rubber disk that supports the jet

Honda PC50 float bowl
missing the rubber disk
that supports the jet

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


2. Keihin PA 00A (PC50) 1973-78 Honda PC50

1973 Honda PC50 and QA50 carburetor illustration

Honda late PC50 carb disassembled

Honda late PC50 carb disassembled

1973-78 Honda PC50

1973-74+ Honda PC50 K1

 

 

 

 

 

Honda PC50 late carb

PC50 K1 (late) carb

 

 

 

 

1973-74 late PC50 carburetor Keihin PA00A

Late PC50 carburetor Keihin PA00A-A

 

 

 

 

 

 

 

 

 

 

 

 


3. Keihin PA M0A (Indian) 1979-84 Indian AMI50

Keihin (Indian) carburetor illustration

The Indian AMI50 Chief four stroke moped engine, with internal pedals, made from 1979-1984, is a copy of an earlier Honda PC50 engine, made from 1967-1978. In the USA, the Honda PC50 “Little Honda” was only made in 1969-70. So parts for Honda PC50 are common in the UK, and maybe Canada, but rare in the US.

1980 Indian AMI-50 black with spoke wheels gold script on tank + sides

1980 Indian AMI-50
PC50 remake engine

Indian with Keihin

 

 

 

 

 

 

The parts list with prices and availability is in the Indian Parts department. 

This Keihin carburetor in the Indian Parts Manual illustration has a push-in main jet, with an thin o-ring seal, a round bowl gasket, a round detached float, and a different float bowl. But the actual Indian carburetor has a M6-0.75 screw-in main jet, an NC50-type bowl gasket, a swinging semi-round float, and a float bowl that looks like an early NC50 float bowl, but it has no choke jet in the corner. 

 

 

 

 

 

 

 

 

 


4. Keihin BB ….. (PA50) on 1977-83 Honda PA50 Hobbit 

Keihin (1978-83 Honda PA50) carburetor illustration

Honda’s successor to the four-stroke PC50 was the two-stroke PA50, known in the USA as Hobbit, and in Europe as Camino. It was made in Belguim by Honda Benelux, so it had a mix of Japanese and European design and componentry. 

1978 Honda PA50II 30mph

1978 Honda PA50II

1978 PA50 carb service

PA50 carb removal

 

 

 

 

 

 

 

This Keihin BB type carburetor is not like any other moped carburetor. It looks more like a Honda generator carburetor. It is a very flat design.   

Servicing: The best way to remove the PA50 carburetor is to hold the back of the bike up by either a rope tied to an overhead beam, or with a milk crate and blocks of wood. Remove the floorboards and side covers. Unplug the ignition wires from the coil at the right rear. Pull them through and move them out of the way. Disconnect the decompression cable and the spark plug cap. Loosen the wiring clamps so there is slack in the wires. Remove the lower rear shock bolts and the swing arm pivot bolt above the engine. Then the whole sub-frame can be moved away from the main frame, either by lifting the back of the bike up, or by swinging it around sideways.

Note that the float bowl can go on two different ways. The wrong way assembles normally, but causes the vertical brass overflow tube to contact the float. Honda designed all of the cleaning ports, drain screws, and adjustment screws to face the right side of the bike, which is the upper left in the exploded view. The drain hose spigot on the float bowl faces the same way as the adjustment screws. The other way to tell is by shaking the carburetor. If you can hear the float rattling inside then the float is not stuck so the float bowl is on correctly. 

While every other moped carburetor is a sliding throttle valve type, this one is a swinging plate throttle valve. The reason is to be flatter, to get more clearance from the bottom of the frame. The manual choke is also a swinging plate, with an automatic release.

Some servicing can be done with the carburetor installed. It is easy to clean the idle passages and jet by spraying a one second long burst of carb spray into the idle mixture screw hole, followed by compressed air. The running engine is allowed to consume the flammable solvent before the next burst is sprayed in, to prevent the engine from getting flooded.

 


5. Keihin PA08B-A or PA08B-B (1977-79 Honda NC50/NA50)

Keihin PA08B-A carb 1977-79 NC50

Keihin PA08B-A carb for 1977-79 NC50
(missing the cable choke assembly)

This carburetor has a throttle cable and a choke cable coming straight up and looping around. It has no vent hoses, vacuum hoses, or oil lines going into it. The oil injection goes into the intake manifold. The float reservoir vent is just a small tube slanting downward.

As with most Honda carburetors, fuel is never allowed to spill onto the engine or anything else. Instead an overflow tube inside the float chamber allows any overflow fuel to flow out and down the drain hose and onto the ground below the engine.  

The 1977-79 Honda NC50 and NA50 each had two carburetor versions, PA08BA and PA08BB. Regardless of the year, or the VIN number, they could have either version. So the customer had to look at the model number stamped into the carburetor, and tell the Honda dealer that number, to get certain parts correct. 

 

 

Honda 1977-80 NC50 carb installed

1977-79 Honda NC50
with PA08BA carb

Honda Express carburetor versions, showing things that are different.

Honda Express carburetor versions, showing things that are different.

 

 

 

 

 

 

 

 

Parts for Sale:  Many new original things like the gasket set and float needle are still available. But the items crossed out are no longer available from Honda. For some of those, Myrons has found or made substitutes.

Some part numbers have been superseded. Those obsolete part numbers are not listed here.  

 

 

Keihin (1977-80 Honda NC50) carburetor illustration

  # price  Honda part #      description              specs   asket and o-ring set
01  $25 16010-143-305 gasket and o-ring set, for A or B
1a1 $05 16010-143-305 top rubber washer for A 10x18x1
1b1 $08 16010-143-305 for B cut the 10x18x1 to 10x16x1
1-2 $10 16010-143-305 intake o-ring 2 x 20 (24 od) 
1-3   $6 16010-143-305 main jet o-ring  1 x 3 (5 od)
1-4 $12  16010-143-305 jet support disk Ø7.5 x 1.8 
1-5 $20 16010-143-305 float bowl gasket
1-6 $08 16010-143-305 drain plug o-ring 2 x 2.5 (6.5 od)
2a  N/A 16011-881-741 float valve A (KL 18-4612) stirrup
2b  $20 16155-883-005 float valve B (KL 18-4068) regular
3a  N/A 16012-147-004 needle jet & needle set
3b  N/A 16012-147-014 needle jet & needle set
3-1 $15 00000-000-000 needle plate substitute Ø3 x 9
3-2 $02 00000-000-000 needle e-clip substutute 1.5
3-3 N/A 00000-000-000 jet needle for A or B 2.0 mm
3a4 N/A 00000-000-000 emulsion tube for type A
3b4 N/A not shown (not replaceable, part of carb body)
4a  N/A 16013-143-620 float set type A stirrup
4b  N/A 16013-147-004 float set type B regular
4-1 $04 00000-000-000 hinge pin substitute Ø2 x 18.5
4-2 $02 00000-000-000 hinge screw M4x5 sunk phillips
5a  N/A 16014-143-620 top cap and washer M20x1
5-1 $25 16014-143-620 top cap A substitute brass
5-1 $25  https://www.motionpro.com/product/01-0033
5b  N/A 16014-147-004 top cap and washer M18x1
5-1 $22 16014-147-004 top cap B substitute plastic
6a  N/A 16015-147-004 float bowl set type A
6b  N/A 16015-147-014 float bowl set type B
6-1 $18 00000-000-000 float drain screw M6x20 special
07  N/A 16016-143-620 adjustment screw set
7-1 $13 00000-000-000 idle speed screw M4x19 special
7-2 $000000-000-000 idle speed screw spring Ø5.5×10
7-3 $16 00000-000-000 idle air screw M6-0.75×20 special
7-4 $12 00000-000-000 idle air screw spring Ø4.8 x 9
08  N/A 16022-143-620 throttle slide & spring
8-1 $20  0000-000-000 throttle slide 13.9 od x 10.0 id
8-2 $15 00000-000-000 throttle slide spring Ø9.5 x 42
09  N/A 16046-143-620 choke top, spring, slide
9-1 $27 00000-000-000 choke top substitute M12-1.0
9-2 N/A 00000-000-000 choke spring
9-3 N/A 00000-000-000 choke slide
10  N/A 16100-147-676 carburetor assembly 1977-79
10  N/A 16100-147-712 carburetor assembly 1980
11
 N/A 16118-166-004 cable rubber boot
12 $01 93500 – 04012 bowl screw M4x12 pan phillips
13 $01 94111 – 04000 lock washer M4 split
14 $02 95001 – 35003 float drain hose 3.5 mm id
15 N/A 95002 – 02070 drain hose clamp B7
16a N/A 99201-081-0780 main jet press-in #78
16b N/A not shown (not replaceable, part of carb body)

 

Keihin NC50 screws

1977-79 NC50 idle adjustment screws
7-1 idle speed screw, tighter is faster idle rpm
7-3 idle air screw, tighter is less air (richer)

Keihin NC50 cable choke substitute

1977-80 NC50 cable choke piece substitute

 

 

 

 

 

 

 

 

 

Main Jet: On a PA08BB the main jet is a tamper-proof tight press-fit type, in the center. The jet cannot be removed, and cannot be replaced.

On a PA08BA the main jet presses or slides in and out, and is supported by a rubber disk. If the disk is missing, the jet can slide downward, allowing fuel to get past the jet o-ring, causing a rich fuel mixture.

Idle Hole Cleaning: Near the engine side of the carb body is a brass tube that dips down into the liquid gasoline. That tube, about 1.5 mm (0.060″) inner diameter and 20mm long, leads to the idle or pilot jet, which is about 0.30 mm (0.012″). The idle jet gets clogged from sitting, then the engine will run but won’t idle. Nothing but a very thin (0.010″) steel guitar string will clean it out. See below about jet drills and cleaning tiny jets. Ultrasonic parts cleaners, carb spray, carb dip, and compressed air are not usually effective. Another way to clean out the idle jet is to 1) place a drill bit that fills the hole (so it does not get crushed), 2) clamp it with a small vise grips, 3) rotate back and forth while pulling, 4) when it comes out, the actual hole is easy to see and clean, 5) press it back in the same way it came out.

Strong solvent is needed to dissolve varnish or tar residue left from years of sitting. Carburetor spray, parts dip, or acetone all help clean out the tar, sometimes with a lot of scraping, brushing or rubbing. Always remember to remove all rubber things first, to not let the rubber touch the solvent. Strong solvents will swell soft rubber, deforming it. Never soak the whole carburetor in strong solvent. In this way, Shaun (at Royal Cyclery and later at Myrons Mopeds) has successfully cleaned out over 100 Honda Express carburetors, without ever replacing any of the rubber gaskets. Part of the reason was they were only sold at Honda dealers, but nonetheless, they are not needed in a normal service or clean-out.

 


6. Keihin PA08E-A (1980 Honda NC50 Express) and PA08D-A (1980 Honda NA50 Express II)

Keihin PA08E-A carb 1980 NC50

Keihin PA08E-A carb for 1980 NC50
(missing top cap and cable choke assy)

The PA08E-A is the same as a PA08B-A, except for three things.

(1) It has an oil injection small hose spigot on the side near the fuel hose spigot.

(2) It has a 18×1 thread top cap, like a PA08B-B has.

(3) It has a Idle Fuel mixture screw, like a PA15A has, instead of an Idle Air mixture screw. See below.

All of the other parts are the same as PA08B-A (push-in jet with o-ring, shallow float bowl with rubber pad holding the jet in). See above.

 

The 1977-79 Honda Express had the oil hose going into the intake manifold. The 1980 and later models had the oil injection hose going into the throttle slide area. There must have been some benefit. 

PA08DA for 1980 NA50

 

The PA08D-A is the same as a PA08B-B, except for two things.

(1) It has an oil injection small hose spigot on the side near the fuel hose spigot.

(2) It has a Idle Fuel mixture screw, like a PA15A has, instead of an Idle Air mixture screw. See below.

All of the other parts are the same as PA08B-B (non-replaceable jet, deep float bowl). See above.

 

 


1981 Honda NC50 Express

1981 NC50 Express (1-spd)

7. Keihin PA15A-A  (1981 Honda NC50) and PA16A-A (1981 NA50)

Keihin PA15A carb 1981 NC50

Keihin PA15A-A carb for 1981 NC50

 

The 1981 Honda Express carburetor features a screw-in main jet, and a built-in vacuum-operated (not electric) automatic choke. When the temperature switch on the head is cold, it allows the engine vacuum to raise the choke plunger up, which opens a new fuel passage, to enrich the mixture during cold starting. As the engine warms up, it closes the vacuum, allowing the thin spring to pull it back down, for normal running. 

 

Keihin PA16A-A carb for 1981 NA50

1981 NA50 Express II (2-spd)

 

The PA16A-A looks identical to the PA15A-A. It is on the 1981 Honda NA50 Express II, the final year of that model.

It is unclear what is different from a PA15A-A.  

After 1983, 50cc Hondas had electric chokes, because they were electric-start scooters with 12 volt batteries. 

 

 

Keihin (1981-83 Honda NC50) carburetor illustration

# price  Honda part #      description              specs   asket and o-ring set
01  $25 16010-190-004 gasket and o-ring set
1-1 $08 16010-143-305 must cut the 10x18x1 to 10x16x1
1-2 $10 16010-143-305 intake o-ring 2 x 20 (24 od) 
1-3 $20 16010-143-305 float bowl gasket
1-4 $08 16010-143-305 drain plug o-ring 2 x 2.5 (6.5 od)
1-5 N/A  16010-143-305 idle fuel mix screw o-ring 1 x 3 (5 od)
0
2
  N/A 16012-GA6-671 needle jet & needle set
2-1 $15 00000-000-000 needle plate substitute Ø3 x 9
2-2 $02 00000-000-000 needle e-clip substutute 1.5
2-3 N/A 00000-000-000 jet needle 2.0 mm
2-4 N/A 00000-000-000 emulsion tube
03  N/A 16013-147-004 float set  regular
3-1 $04 00000-000-000 hinge pin substitute Ø2 x 18.5
3-2 $02 00000-000-000 hinge screw M4x5 sunk phillips
0
4  N/A 16014-190-014 top cap with curved pipe 1981
04  N/A 16014-187-013 top cap with curved pipe 1982-83
05  N/A 16015-147-014 float bowl set 
5-1 $18 00000-000-000 float drain screw M6 x 20 special
06  $20 16016-191-004 idle fuel adjustment screw set
6-1 N/A 00000-000-000 idle fuel mixture screw M6-0.75 x 20 special
6-2 N/A 00000-000-000 idle fuel mix screw spring Ø5 x 9
6-3   $6 00000-000-000 idle fuel mix screw o-ring  1 x 3 (5 od)

6-4   $3 00000-000-000 idle fuel mix screw washer 3.1 x 5.0 x 0.5
07  N/A 16022-143-620 throttle slide & spring
7-1 $20  0000-000-000 throttle slide 13.9 od x 10.0 id
7-2 $15 00000-000-000 throttle slide spring Ø9.5 x 42
08  N/A 16028-187-003 idle speed screw and spring
8-1 $13 00000-000-000 idle speed screw M4x19 special
8-2   $8 00000-000-000 idle speed screw spring Ø5.5×10
09  N/A 16100-190-672 carburetor assembly 1981
09
  N/A 16100-GA6-671 carburetor assembly 1982-83
10
  N/A 16118-190-004 cable curved rubber boot (1981)
10  N/A 16118-187-003 cable curved rubber boot (82-83)
11  $25 16155-883-005 float needle valve (KL 18-4068)
12
  N/A 16199-435-771 float drain hose
13  N/A 16608-GA6-670 control valve tube 4
14  $01 93892-04012-08 screw & washer M4x12 pan phillips
15  N/A 95002-02070 hose clamp B7 
16  N/A 95002-02080 hose clamp B8
17  N/A 95002 – 02650 hose clamp B6.5
18  N/A 95005 – 35001 float vent hose 3.5 mm id
19  N/A 99101-187-0750 jet #75 (KL 18-9791) M6-0.75 thread
19  N/A 99101-187-0780 jet #78 (KL 18-9792) 

19  N/A 99101-187-0800 jet #80 (KL 18-9793) 

 

Keihin late NC50 adjustment screws

1980-83 NC50 idle adjustment screws
8-1 idle speed screw, tighter is faster idle rpm
6-1 idle fuel screw, tighter is less fuel (leaner)

 

 

 

 

 

 

 

 

 

 

Float Valve Seat: On these carburetors the float seat (the cup that the float needle valve slides in) is carved into the actual carburetor body, and is not replaceable. Polish it with a spinning Q-tip and polish, such as Turtle Wax. There is a choke jet, pressed into a corner of the float bowl. When it gets clogged the engine will only start easily when it is warm.

Verify all jets and fuel or air passageways are open, using wires and or visually with carb spray (wear goggles). 

 

Cable Differences: You can tell what year range a Honda Express is from a distance. A 1977 to 1980 has two cables, a throttle and a choke cable coming straight up from the carburetor.  A 1981 has just a throttle cable coming straight up, but also a vacuum hose for the choke and a float vent hose.  A 1982 to 1983 has a black plastic curved elbow on top, that redirects the throttle cable forward and down, a vacuum hose for the choke, and a vent hose. A 1982-83 also has a different frame, a low headlight, and a two speed transmission.

The Honda Express throttle cable curves rearward and loops downward to get below the carburetor, and then goes forward into the frame tube. The loop design adds friction, but it makes a good clean step-thru frame without any cables or wires hanging out.  

The 1981-83 automatic choke plunger mechanism itself is not replaceable.  

 

 

 

 

 

 

 

 

 

 


8. Keihin PA13E-A (’81-82 Honda NX50, ’82-83 NC50/NU50)

Keihin PA13E-A carb Honda NX50

Keihin PA13E-A carb Honda NX50, NU50, 82-83 NC50

This is the most sophisticated moped carburetor, and also the one with the most hoses.

Keihin (1982-83 Honda NU50) carburetor illustration

 

 

 

 

 

 

 

1982-83 NC50 hoses

1982-83 Honda NC50, NU50 hoses explained

1982 Honda NU50 Urban Express

1982 NU50 Urban Express

 

 

 

 

 

 

 

1982 Honda NX50 Express SR

1982 NX50 Express SR

 

 

 

 

 

 

 

This PA13E-A carb is the same as the previous PA15A-A carb, except for stud bolts instead of holes on the mounting flange. So all of the parts are the same. See above.

 


9. Keihin (NQ50/NM50) on 1984-88 Honda NQ50 Spree and 1983-86 Honda NM50 Aero

Keihin (1985-87 Honda NM50) carburetor illustration

These were zippy 50cc two-stroke automatic scooters that maxed out at 30mph to meet many US state’s moped laws. They have electric start so there is 12 volt battery power to operate an automatic electric choke. They also have a gas gauge and an automatic vacuum petcock on the gas tank. You don’t have know very much to operate one. They had a CVT variator that continuously changes the belt drive pulley size ratio, for very quick acceleration. 

1983 Honda NM50 Aero

1983 Honda NM50 Aero

1985 Honda NQ50 Spree

1985 Honda NQ50 Spree

 

 

 

 

 

 

 

Except for the PA50 carb, all of these Keihin carburetors from 1977 to 1987 look similar. Many things are the same. Some things are subtly different. Those details are not covered here, at least yet. More parts for sale and info will follow.

 

 

 

 

 

 

 


Gasket Set Differences

 

16010-143-620 for PA08B-A
top rubber washer 10x18x1
intake o-ring 2 x 20 (24 od) 
main jet o-ring  1 x 3 (5 od)
jet support disk Ø17.5 x 1.8 
float bowl gasket
drain plug o-ring 2 x 2.5 (6.5 od)

 

16010-147-711 for PA08B-B and PA08E-A  (was 16010-147-004)
top rubber washer 10x16x1
intake o-ring 2 x 20 (24 od)  

float bowl gasket
drain plug o-ring 2 x 2.5 (6.5 od)

 

16010-190-004 for PA15A-A and PA13E-A
top rubber washer 12x16x1 ?
intake o-ring 2 x 20 (24 od)
idle mix screw o-ring 1 x 3 (5 od)
float bowl gasket
drain plug o-ring 2 x 2.5 (6.5 od)

 

 

The above gasket sets listed in the parts catalog have all sold out. But there is a “universal” Honda Express gasket set still available. Thanks to Matt at Honda Suzuki World in Oakland, Maine for this:

16010-143-305 for PA08B-A, but fits all, except for the top washer
top rubber washer 10x18x1 (can cut to 16)
intake o-ring 2 x 20 (24 od) 
jet or idle screw o-ring 1 x 3 (5 od)
jet support disk Ø17.5 x 1.8 
extra o-ring  2 x 18 (22 od)
float bowl gasket
drain plug o-ring 2 x 2.5 (6.5 od)

 

Where else to get Keihin parts: There is a Honda dealership in Oakland, Maine USA, with a dedicated employee, Matt McGowan who appreciates small Honda and Suzuki motorcycles. Matt can still get many parts for Honda NC50/NA50 Express, Suzuki FA50 Shuttle, and more. His shop has every US dealer’s parts inventories at their fingertips, to locate scarce parts. Call for parts inquiries at (207) 465 – 3710, 9am to 5pm eastern time, ask for Matt, or email to hondasuzukiworld@yahoo.com or click http://www.hondasuzukiworld.com/contact-us/contact-us.html.


Jet Drills

January 27, 2007

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, 0.011″ (eleven 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.

This will help you visualize how small these drills and jets are!

Moped main jets range from 0.018″ (#77 drill) to 0.026″ (#71 drill). 

Moped idle jets, like Tomos A55, are 0.011″ (smaller than #80).

An average human hair is 0.003″ (three thousandths of an inch).

So moped jet holes are 4 to 9 hairs wide!

Shauns well used jet drill container from the 1980's

Shaun’s well used drill container from 1987

 

Jet Drills: All through the late 1980’s and 1990’s, Shaun (at Royal Cyclery and later at Myrons Mopeds) used the USA-made jet drills to service carburetors. The drill sizes are an American wire gauge. They did not vary in size. Those 20-piece Drill Sets 61 to 80, cost $40 in 2015, $33 in 1998. and $29 in 1987. Some are in clear plastic round dome containers, and some are in conventional metal drill set boxes.

 

Drill Set 61-80 USA-made

Drill Set USA-made

Jet Drills made in China

Set 1 China-made

China-made Drills: In the 2000’s there were many China made tools sold in “surplus” tool stores. The China made 20-piece Drill Sets 61 to 80, sell for $7 to $10, or one fourth as much. They have an excellent blue plastic container, that only lets out one at a time. But the drill sizes are all wrong. From about 2010 to 2014, Myrons Mopeds sold these inexpensive drill sets, not knowing that the drill sizes were inexact, to say the least.

So although the China sets cost one forth as much, they only have about seven or eight different sizes, and they lack the smaller sizes below 0.4 (or sometimes 0.6) mm. Each set is different.

 

Jet Drills made in USA

Jet Drills made in USA

Set 2 China-made

Some have poorly made drills, twisted funny, bigger at the cutting end, or lumpy, varying in thickness. Some have poorly made cutting tips, so they might wander, grab and break, or not cut well.

Despite the poor quality and inexactness, the inexpensive drills are still useful for cleaning purposes, but not for measuring and maybe not for drilling. Fortunately, brass carburetor jets are the easiest thing to drill, with a drop of oil and a pilot hole already there.

 

 


Micro Drills and Wires for Sale Individually

These drills are measured at the shank (the smooth part). At the cutting edge they are 1 or 2% bigger.

These wires are steel guitar strings, cut into 5 inch lengths. 

“Metric” jets have a number that literally means hundredths of a millimeter, so a 64 jet is 0.64 mm.

Micro Drills for sale

inch   mm/#  price     moped jets that it cleans
0.011   wire     N/A Gurtner Motobecane diffuser – two idle holes (.013)
0.0135 #80  $3.50
0.0145 #79  $3.50
0.0157 0.40  $2.00 Dellorto 38 (.0162), Bing 42 (.0162)
0.016   #78  $3.00 Dellorto 40 (.0168), Bing 44 (.0167)
0.017   wire  $0.50 Dellorto 42 (.0177), Bing 46 (.0175)
0.018   #77  $3.00 Dellorto 44 (.0186), Bing 50 (.0188)
0.019   ——  $1.50 Dellorto 46 (.0194), Bing 52 (.0194)
0.0197 0.50  $1.50 Dellorto 48 (.0202), Bing 54 (.0200), “Metric” 51 (.0201)
0.0200 #76  $1.50 Dellorto 49 (.0207), Bing 56 (.0206), Gurtner 210=52 (.0210)
0.021   #75  $3.00 Dellorto 51 (.0215), Bing 58 (.0213), Gurtner 220=54 (.0220)
0.0225 #74  $1.50 Dellorto 55 (.0231), Bing 62 (.0229), Gurtner 230=56 (.0230)
0.023   ——  $1.50 Dellorto 56 (.0235), Bing 64 (.0234), Gurtner 240=58 (.0236)
0.0235 0.60  $1.50 Dellorto 58 (.0242), Bing 66 (.0239), Gurtner 250=60 (.0242)
0.024   #73  $1.50 Dellorto 60 (.0247), Bing 68 (.0248), “Metric” 63 (.0248)
0.025   #72  $3.00 Dellorto 62 (.0255), Bing 70 (.0254), “Metric” 65 (.0256)
0.026   #71  $3.00 Dellorto 66 (.0268), Bing 74 (.0267), “Metric” 68 (.0268)
0.0275 0.70  $1.50 Dellorto 70 (.0280), Bing 78 (.0280), “Metric” 71 (.0280)
0.028   #70  $1.00 Dellorto 72 (.0287), Bing 80 (.0287), “Metric” 73 (.0287)
0.0292 #69  $2.50 Dellorto 78 (.0306), Bing 84 (.0301), “Metric” 77 (.0303)
0.030   wire     N/A Dellorto 80 (.0312), “Metric” 79 (.0311), Gurtner K80 (.0311)
0.031   #68  $1.00 Dellorto 82 (.0318), “Metric” 81 (.0319)
0.0315 0.80  $1.00 Dellorto 84 (.0324), “Metric” 82 (.0323)
0.032   #67  $0.75 Dellorto 86 (.0331), “Metric” 84 (.0331)
0.0325  —— $1.00 Dellorto 88 (.0337), “Metric” 86 (.0339)
0.033   #66  $2.50 Dellorto 90 (.0343), “Metric” 88 (.0346)
0.034   wire     N/A “Metric” 90 (.0354)
0.035   #65  $1.00 “Metric” 92 (.0362), Gurtner MB (side mount) diffuser (.0358)
0.0354 0.90  $1.00 “Metric” 94 (.0370)
0.036   #64  $2.50
0.037   #63  $2.50
0.038   #62  $1.00
0.039   #61  $0.75
0.0394 1.00  $0.75

 


Deluxe 40-piece Micro Drill Set

Jet Drills 80-72 and 71-60

Myron’s Mopeds two case deluxe micro drill set, 80 to 72 (small) and 71 to 60 (large) plus many in-between sizes.
Price $45

Slide clear top plastic until hole is over drill (and pointer is on desired drill number). Only lets one drill out at a time. Never take out more than one at a time, or they can get mixed. The case keeps them organized. If any get lost, dull, or broken, individual drills can be bought at some hardware stores for $2-$4 each.

Useful for sizing to tell how big a jet really is (sometimes they’re drilled out or labeled wrong).

Useful for cleaning varnish or corrosion coating the inside of an old jet. It doesn’t really clean out any other way. The drill is used as a file, held with a needlenose pliers.

Useful for drilling jets to make a new size, as an alternative to buying ones. The drill is held with a needlenose pliers, and the jet is rotated with your fingers, with a drop of oil. To go down in size, fill the hole with solder and re-drill it smaller.

 

 

 


Other Tools for Cleaning Jets

Using a micrometer to measure a 0.017 wire

Using a micrometer to measure a 0.017″ wire

Guitar steel string 17 thousandths of an inch

Guitar string

Guitar Steel Strings in the smaller sizes are excellent tools for cleaning small holes. Here is a 0.0170 inch steel wire guitar string, perfect for cleaning out a 1974-85 Tomos stock jet size 46 that has a 0.0175 inch hole. A Honda Express NC50 (Keihin) carburetor, has a long brass idle jet tube with a tiny jet hole at the far end, too far for a drill to reach. For that, only a 2 or 3 inch piece of 0.010″ steel guitar string will reach to clean it. Ultrasonic cleaners, carb spray, or soaking are not effective for that. Other examples are a Sachs 52 jet 0.0190 would be cleaned by a 0.018″ wire, or a Motobecane 230 jet 0.023″ would be cleaned by a 0.022″ wire. The wire has to be a little smaller than the hole. Plain steel strings range from 0.008″  to 0.017″ in steps of 0.001″. Wound strings range from 0.017″ to 0.065″. 

 

Torch Tip Cleaner Set

Torch Tip Cleaner Set

Root Canal Files

Root Canal Files (say ahhh)

Welding Torch Tip Cleaners are another excellent tool for cleaning small holes. The tip has a cutting surface but not the sides. So it is made to clean the hole without widening it.

Wire Feeler Gauge Sets: There are also wire gauge measuring sets that look the same as the torch cleaner set shown.

Dentist’s Root Canal Files are also good for cleaning small holes. Color coded files range from 0.06 to 1.10 mm (0.0024 to 0.0433 inch).