3. Keihin Parts for 1977-83 NC50, NA50, NX50, NU50

April 3, 2021

== carb ID# ============  M O P E D S  ===========
6.
PA 08B-A  1977-78 Honda NC50 Express xxx    30 mph TS
6. PA 08B-B  1977-79 Honda NC50, NA50  xxxx    30 mph TS
6. PA 08C-A  1978-79 Honda NC50, NA50  xxxx   
30 mph TS
6. PA 08E-A  1980-80 Honda NC50 Express xxx    30 mph TS
6. PA 08E-B  1980-80 Honda NC50 Express xxx    30 mph TS
6. PA 08D-A  1980-80 Honda NA50 Express II x   30 mph TS
7. PA 12A-A  1981-81 Honda NCZ50 Moto Compo

7. PA 15A-A  1981-81 Honda NC50 Express xxx    30 mph TS
7. PA 16A-A  1981-81 Honda NA50 Express II  x   30 mph TS
7. PA 13B-A  1981-82 Honda NX50 Express SR x   30 mph TS
7. PA 13B-B  1982-83 Honda NC50 Express xxx     30 mph TS

7. PA 13E-A  1982-83
Honda NU50 Urban Express 30 mph TS
7. PA 25A-A  1982-83 Honda NC50AA, NU50AA    25 mph TS

 

 

 

 

 


6. Keihin
size     carb  model code  year 00 frame number range  000  model
∅12 PA08B-A or B #147 1977 NC50-1139281 to 0000000 NC50 Express (US)    30 mph
∅12 PA08B-A or B #147 1978 NC50-2000013 to 0000000 NC50 Express (US)    30 mph
∅12 PA08E-A or B #147 1979 NC50-2100011 to 0000000 NC50 Express (US)    30 mph

∅12 PA08E-A or B #147 1980 NC50-2200005 to 0000000 NC50 Express (US)    30 mph
∅12 PA08B-B    on #163 1979 AB01-5000001 to 0000000 NA50 Express II (US) 30 mph

∅12 PA08D-A    on #163 1980 AB01-5200001 to 0000000 NA50 Express II (US) 30 mph

 

1977 Honda NC50 Express

1978 Honda NC50 Express

’79 NC50 Express

 

 

 

 

 

 

 

 

 

1980 Honda NC50 Express

1980 Honda NA50 Express II

 

 

 

 

 

 

 

 

 

 

 

#0  16100-147-675
Keihin PA08B-A

#0 16100-147-676
Keihin PA08B-B

#0 16100-147-711
Keihin PA08E-A

 

 

 

 

 

 

 

 

 

#0 16100-147-712
Keihin PA08E-B

16100-163-771
Keihin PA08D-A

 

 

 

 

 

 

 

 

Flange Mount: 38 mm hole spacing. 2 x 20 (24 od) intake o-ring.

Honda Express carburetor versions, showing things that are different.

Honda Express carburetor versions

Cable choke: 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, PA08B-A and PA08B-B. 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. 

Oil injection hose location: The 1977-79 Honda Express had the oil hose going into the intake manifold, not the carburetor. The 1980 and later models had the oil injection hose going into the carburetor at the throttle slide area. There must have been some benefit, like maybe throttle slide lubrication.

16010-143-620
has a, c, d, e, f, g
for PA08 BA

16010-143-305
a, c, d, e, f, g, h, i 
for PA08 BA

16010-147-004
has b, c, f, g
for PA08 BB, EB

16010-147-711
has b, c, d, f, g
08 BB EB DA EA

16010-147-505
has b, c, d, f, g, i
08 BB EB DA EA

 

 

 

 

 

 

 

 

 

    quantity
o#
⇓⇓⇓⇓⇓ 
Keihin PA(a)08BA (b)08BB (c)08EA (d)08EB (e)08DA 
o# abcde price  Honda part#x  description xxx specs
10 1ooooN/A 16100-147-673 

10 1ooooN/A 16100-147-675 carburetor 77-79 NC50 PA 08B-A
10 o1oooN/A 16100-147-676 carb 77-79 NC50 NA50 PA 08B-B
10 oo1o0N/A 16100-147-711 carburetor 
1980 NC50 PA 08E-A
10 oo01o  N/A 16100-147-712 carburetor 
1980 NC50 PA 08E-B
10 oooo1N/A 16100-163-771 carburetor  1980 NA50 PA 08D-A

o1 10ooo $21 16010-143-620 gasket solo-set   1a o c d e f g
o1 10ooo $23 16010-143-305 gasket multi-set  1a o c d e f g h i

o
1 01o1o $23 16010-147-004 gasket solo-set   oo b c o o f g
o1 o1111 $23 16010-147-711 gasket solo-set   oo b c d o f g
o1 o1111 $21 16010-147-505 gasket multi-set oo b c d o f g o i

1a 100o0 $$3 00000-000-000 top rubber washer 10 x 18 x 1
1b o1111 $$8 00000-000-000 top rubber washer 13 x 16.5 x 1
1c 11111 $$2 00000-000-000 intake o-ring 2 x 20 (24 od) 
1d 1o1o1 0$2 16176-551-004 jet or screw o-ring 1 x 3 (5 od)
1e 1o0oo $10 16197-063-004 jet support pad disk Ø7.5 x 1.8
1f 11111 $15 00000-000-000 float bowl gasket  Ø1.5 NC50-type
1g 11111 $$2 00000-000-000 drain plug o-ring 1.5 x 4 (7 od)
o2 1oo1o $21 16011-881-741 float needle valve  stirrup
o2 o11o1 $22 16155-883-005 float needle valve regular
o3 1o1o0  N/A 16012-147-004 needle set 3a 3b 3c 3d 08BA EA
o3 ooooo $22 16012-130-640 needle set 3a 3b 3c 3d PA 03A-A
o3 ooooo $22 16012-165-014 needle set 3a 3b 3c 3d PA 03B-A

o3 o1o11 $15 16012-147-014 needle set 3a 3b 3c 08BB EB DA
3a 11111 0$5 16156-044-004 jet needle w-clip
3b 11111 0$2 16157-044-004 jet needle e-clip 1.5 for Ø2.0 needle
3c 11111 $10 00000-000-000 jet needle Ø2.0 D348 thick 08B-A,
3c 11111 $10 00000-000-000 PA 08B-B, 03A-A, 00A, 01A

3c ooooo $10 00000-000-000 jet needle Ø2.0 D117 thin 03B-A,
3c ooooo $10 00000-000-000 PA 03C-A, 03D-A, 03H-B, 03M-A, etc
3d 1o1oo  N/A 00000-000-000 needle jet (emulsion tube) 08BA 08EA
3d o1o11  N/A 00000-000-000 needle jet & jet fixed 08BB 08EB 08DA

3d ooooo $10 00000-000-000 needle jet (emulsion tube) PA 03A-A
3d ooooo $10 00000-000-000 needle jet (emulsion tube) PA 03B-A
o
4 1oo1o  N/A 16013-143-620
o4 1oo1o  N/A 16013-099-691 float set 4a oo 4c 4d black stirrup
o4 o11o1 $28 16013-147-004 float set oo 4b 4c 4d white regular
4a 1oo1o  N/A 00000-000-000 float bare, solid black foam stirrup
4b o11o1 $21 00000-000-000 float bare hollow white plastic regular
4c 11111 $$4 00000-000-000 hinge pin substitute Ø2 x 18.5
4d 11111 $$3 0-93600-04006 hinge screw M4x6 sunk phillips

1977-79 NC50 idle adjustment screws
7a idle speed screw, tighter is faster
7c idle air mix screw, tighter is richer

o5 1oooo $23 16014-143-620 top set substitute 5a 1a M20-1.0
o5 o1111 $22 16014-147-004 top set substitute 5a 1b M18-1.0
o6 1ooooN/A 16015-147-004 chamber set A 6a oo 6c 1e 1f 1g for jet pad
o6 o1111  N/A 16015-147-014 chamber set B oo 6b 6c oo 1f 1g for no pad
6a 1oo0oN/A 16015-147-004 float bowl A shallow with pad holder
6b o1111  N/A 16015-147-014 float bowl B shallow, no jet pad holder
6c 11111 $16 00000-000-000 
float drain screw M6x20 special
o7 11o1o $15 16016-143-620 screw set 7a b c d idle air
o
7 oo101  N/A 16016-147-711 screw set 7a b o d e f g idle fuel

7a 11111 $$4 00000-000-000 idle speed screw M4x19 special
7b 11111 $$2 00000-000-000 idle speed screw spring Ø5.6 x 10
7c 11o1o $$6 00000-000-000 idle air screw M6-0.75 thick tip
7d 11111 $$7 00000-000-000 idle air or fuel spring Ø4.8 x 9
7e oo1o1  N/A 00000-000-000 idle fuel screw M6-0.75 thin tip
7f  oo1o1 $$3 00000-000-000 idle fuel screw washer 3.1 x 5.0 x 0.5
7g oo1o1 0$2 16176-551-004 idle fuel screw o-ring 1 x 3 (5 od)

1980-83 NC50 idle adjustment screws
7a idle speed screw, tighter is faster 
7e idle fuel mix screw, tighter is leaner

o8 11111 $38 16022-143-620 valve set 8a, 8b
8a 11111 $22 00000-000-000 throttle slide Ø13 #15A
8b 11111 $12 00000-000-000 throttle spring original Ø9.5 x 42
8b
11111 $$7 00000-000-000 throttle spring substitute shorter, stiffer
o9 11111 $25 16046-147-004 choke set substitute 9a 9b 9c
9a 11111 $10 00000-000-000 choke top substitute plastic M12-1.0
9a 11111 $15 00000-000-000 choke top substitute metal M12-1.0
9b 11111 $$4 00000-000-000 choke spring substitute
9c 11111 $12 00000-000-000 choke slide substitute
11 11111 $2.00 16118-166-004 rubber boot substitute Dellorto
12 22222 $1.00   93500-04012 bowl screw M4x12 pan phillips
13 22222 $0.20   94111-04000 lock washer M4 split
14 11111 $1.00 95001 – 35003 hose substitute 1/8 x ¼ 3.1 x 6.3

1977-80 NC50 cable choke top substitute

15 11111  N/A 95002 – 02070 drain hose clamp B7 (for 7 not 6.3)
16 10o0o  
N/A 99201.081.0780 push-in jet 78 08BA

16 10o0o $23 substitute jet, #70 drilled to 78 08BA
16 01111 N/A fixed needle jet & jet pressed in 08BB EA EB DA
this jet is 0.78mm 0.0307″, cleaned with a #69 drill 0.0292″     

 

Main Jet: On PA08BB, EA, EB and DA versions the main jet is a tamper-proof tight press-fit type, in the center. The jet cannot be removed, and cannot be replaced. It is 0.78 mm – 0.0307″, and can be cleaned perfectly with a #69 drill 0.0292″.    

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.

Keihin PA08C-A: This is approximately for a 1979-80 NC50, or maybe NA50. It is identical to a PA08B-B. It has the same white float, non-stirrup float needle, fixed jet, 18mm top threads, and same gaskets. The idle mixture screw type is unknown. No photo available. 

 


7. Keihin
size  carb  model code  years       models
∅12 PA12A-A on #GC6 1981-81 Honda NCZ50 Moto Compo
∅12 PA15A-A on #190 1981-81 Honda NC50 Express (US) xxxxx xxxx 30 mph
∅12 PA16A-A on #193 1981-81 Honda NA50 Express II (US) xxxx xxx  30 mph

∅12 PA13B-A on #187 1981-82 Honda NX50 Express SR (US) xxxx xx  30 mph
∅12 PA13B-B on #GA6 1982-83 Honda NC50 Express (US) xxxxx xoxx 30 mph

∅12 PA13E-A on #GC1 1982-83 Honda NU50 Urban Express (US) xxxx 30 mph

∅12 PA13E-A on #GC1 1982-83 Honda NU50M Urb. Expr. Deluxe (US)  30 mph
∅11 PA25A-A on #GA6 1982-83 Honda NC50AA Express (Iowa) xxxxxx25 mph
∅11 PA?????   on #GC1 1982-83 Honda NU50AA Urban Express (Iowa)   25 mph
∅10? PA25A-A on#GC1 1982-83 Honda NU50MA Urb. Ex. Deluxe (Iowa) 25 mph

 

1981 NC50 Express

1981 NA50 Express II

1981 NX50 Express SR

1982 NU50 Urban Express

 

 

 

 

 

 

 

 

#0   16100-GC6-003  Keihin PA12A-A 

16010-187-003 gasket set

 

 

 

 

 

 

 

 

#0  16100-190-672
Keihin PA15A-A

#0  16100-193-672
Keihin PA16A-A

#0  16100-187-673
Keihin PA13B-A

 

 

 

 

 

 

 

 

#0 16100-GA6-671
Keihin PA13B-B

#0 16100-???-???
Keihin PA25A-A

#0  16100-GC1-671
Keihin PA13E-A

 

 

 

 

 

 

 

 

Flange Mount: 38 mm hole spacing, 2 x 20 (24 od) o-ring on NC50, NA50 (PA15A-A, PA16A-A, PA13B-B)
Flange Mount: 32 mm stud spacing, 2 x 18 (22 od) o-ring on NX50, NU50, NU50M (PA13B-A, PA13E-A)
Flange Mount: 36 mm hole spacing, 2 x 20 (24 od) o-ring on NC50I, (PA25A-A)

Vacuum-operated automatic choke: These carburetors feature 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. The more precise term for this is “automatic vacuum operated cold start fuel mixture enrichment device”. The 1981-83 automatic choke device itself is not replaceable.

The vacuum source hose has a check ball valve that only allows air flow into the carburetor venturi, and not back out. It needs this even though there is reed valve, because there is still some residual reverse flow caused by the forward and reverse motion of the piston.

The vacuum choke that came out in 1981 did not last long. After 1983, 50cc on-road Honda’s had electric chokes, because they were electric-start scooters with 12 volt batteries. 

Identical twins: The PA16A-A looks identical to the PA15A-A. It is on the 1981 Honda NA50 Express II, the final year of that USA-only model. They both have 38 mm flange hole spacing, #75 screw-in jet, 20 mm intake o-ring and the non-stirrup type B float needle. The only difference is the top cable curved pipe. On a PA15A-A it is permanently attached to the screw-on top cap with a swivel joint, while on a PA16A-A the curved cable pipe is detachable.

Intake studs: After 1981 these carbs had studs instead of threaded holes in the mounting flange, except for PA25A-A. PA13B-A and PA13E-A studs are spaced 32 mm with a 18mm intake o-ring. PA13B-B studs are spaced 38 mm, with a intake o-ring 20 mm. 

Iowa carb: The PA25A-A is like a PA13B-A, with M18-1.0 top cap threads, vacuum-operated automatic choke, choke jet in float bowl, tall 2.5 x 1.5 float bowl gasket, intake o-ring 20 mm, non-stirrup type float and float needle, screw-in main jet size 75. The only noticeable difference is the absence of studs.

Iowa cylinder: The exhaust port is restricted. Here left is 49-state, right is Iowa.

#1 16010-190-004
for 15A 16A 13BB 25A

#1 16010-187-003
for PA 13BA 13EA

#1  16010-GF8-305 for
for PA 13BA 13EA

 

 

 

 

 

 

 

 

 

PA 15AA 16AA 13BA 13BB 13EA

      quantity
o#
⇓⇓⇓⇓⇓⇓ 
PA (a)15AA (b)16AA (c)13BA (d)13BB (e)25AA (f)13EA
o# abcdef price  Honda part#x  description xxx specs
00 1o0000  N/A 16100-190-672 carburetor ’81-81 NC50 PA15A-A
00 o10000  N/A 16100-193-672 carburetor ’81-81 NA50 PA16A-A
00 o01000  N/A 16100-187-673
carburetor ’81-82 NX50 PA13B-A
00 o00100  N/A 16100-GA6-671 carburetor ’82-83 NC50 PA13B-B
00 o0001N/A 16100-
GA6-671 carburetor ’82-83 NC50AA PA25A-A
00 o0000
N/A 16100-GC1-671
carburetor ’82-83 NU50 PA13E-A
01 001
001 $24 16010-187-003 gasket solo-set   1b o d g h k
01 110110 $24 16010-190-004 gasket solo-set   1b c d g o k
01 001001 $25 16010-GF8-305 gasket multi-set 1b o d g h k t u

1b 111111 $$8 00000-000-000 top rubber washer 13 x 16.5 x 1
1c 110110 $$2 00000-000-000 intake o-ring 2 x 20 (24 od) 
1d 111111 0$2 16176-551-004 idle fuel screw o-ring 1 x 3 (5 od)
1g 111111 $$2 00000-000-000 drain plug o-ring 1.5 x 4 (7 od)

1h 001001 $$2 00000-000-000 intake o-ring 2 x 18 (22 od)
1k 111111 $22 00000-000-000 float bowl gasket 2.5 tall by 1.5 wide
02 0010?0  N/A 16012-187-671 needle set 2a 2b

02 1100?0  N/A 16012-193-671 needle set 2a 2b 2c 2d
02 0001?1  N/A 16012-GA6-671 needle set 2a 2b 2c oo 2e

02 0000?1  N/A 16012-GC1-671 needle set 2a 2b 2c oo 2f

2a 111111 0$5 16156-044-004 jet needle w-clip
2b 111111 0$2 16157-044-004 jet needle e-clip for 1.5 clip groove
03 111111 $28 16013-147-004 float set white 3a 3b 3c
3a 111111 $21 00000-000-000 float bare white plastic regular
3b 111111 $$4 00000-000-000 hinge pin substitute Ø2 x 18.5
3c 111111 $$3 0-93600-04006 hinge screw M4x6 sunk phillips
04 1o0000  N/A 16014-190-014 top set NC50 fixed cable pipe M18-1.0
04 o10000 $24 16014-147-014 top set NA50 detachable pipe M18-1.0
04 o01110  N/A 16014-187-013 top set NX50, 82-83 NC50 M18-1.0

04 o00001  N/A 16014-GB2-003
04 o00001  N/A 16014-GB0-831 

04 o00001  N/A 16014-098-980 top set NU50 fixed cable pipe M18-1.0

05 110000  N/A 16015-191-034 chamber set deep bowl with choke jet
05 001000  N/A 16015-187-671 chamber set deep bowl with choke jet
05 0001?0  N/A 16015-GA6-671 chamber set deep bowl with choke jet

05 0000
?N/A 16015-187-043 chamber set deep bowl with choke jet
06 000111 $32 16016-191-004 idle fuel screw set
06 111000 $32 16016-187-003 idle fuel screw set

6e 111000  N/A 00000-000-000 idle fuel mixture screw M6-0.75 special
6b 111111 $$7 00000-000-000 idle fuel mix screw spring Ø5 x 9
6f  111111 $$3 00000-000-000 idle fuel mix screw washer 3.1×5.0x0.5
07 111111 $0016028-187-003
07 111111 $15 16028-GC8-004 idle speed screw and spring 7a 7b

7a 111111 $$4 00000-000-000 idle speed screw M4x19 special
7b 111111 $$2 00000-000-000 idle speed screw spring Ø5.5×10
08 1100?0 $38 16022-143-620 throttle slide & spring
08 0010?1  N/A 16022-187-731 throttle slide & spring
08 0001?1 
N/A 16022-191-004 throttle slide & spring
8a 110000 $22 00000-000-000 throttle slide Ø13 #15A
8b 110000 $12 00000-000-000 throttle slide spring Ø9.5 x 42

NC50 idle fuel screw
top: original 
bottom: replacement

10 100000  N/A 16118-086-004
10 100000  N/A 16118-166-004 cable rubber boot
10 101110  N/A 16118-187-003 cable rubber boot
10 00000N/A 16118-GB4-003 cable rubber boot

11 111111 $22 16155-883-005 float needle valve KL 18-4608
12 110110  N/A 16199-435-771 overflow hose 3.0 x 6.5
12 00100N/A 16199-187-003 
12 00100N/A 16198-HC0-405 overflow hose 3.0 x 6.5
13 001000  N/A 16608-187-000 control hose with check ball 5 x 10

13 110000  N/A 16608-193-670 control hose with check ball 5 x 10
13 000110  N/A 16608-GA6-670 control hose with check ball 5 x 8

13 00000N/A 16608-GC1-000 control hose with check ball 5 x 8

14 222222 0$1 93892-04012-08 screw & washer M4x12 pan phillips
15 111111  N/A 95002 – 02070   hose clamp B7 vacuum source hose
16 111000  N/A 95002 – 02100   hose clamp B10 for control hose
16 000111  N/A 95002 – 02080   hose clamp B8 for control hose

17 111111  N/A 95002 – 02650   hose clamp B6.5 for overflow hose
18 111111  N/A
 95005 – 35001   vacuum (source) hose 3.5 x 7 x 130
19 oo0010 $$7 99101-187-0700 screw-in jet #70 M6-0.75 PAMOA PA25A ? 78-80 Indian, 82-83 NC50I
19 110100 0$7 99101-187-0750 screw-in jet #75 M6-0.75 PA15A 16A 13BB 81-83 NC50, 81 NA50
19 oo1000 0$7 99101-187-0780 screw-in jet #78 M6-0.75 PA13BA 81-82 NX50
19 oo0001 0$7 
99101-187-0850 screw-in jet #85 M6-0.75 PA13EA 82-83 NU50

 

 

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. 

Choke jet: On all of these NC50-type carbs, both shallow and deep-float-bowl versions, 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.  

1982-83 NC50 hoses

Comparison of PA MOA-A, PA 08B-B, PA 08B-A, and PA 15A-A

 

 

 

 

 

 

 

 

 

Keihin idle mixture screw channels
Left PA08B-B with idle air screw
Right PA15A-A with idle fuel screw

 

 

You can tell the difference between a carb with an idle air mixture screw, and a carb with an idle fuel mixture screw, by the shape of the casting at the top of the float chamber.

 

 

 

 

 

 

 

 


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  $6.00
0.0145 #79  $5.00
0.0157 0.40  $3.00 Dellorto 38 (.0162), Bing 42 (.0162)
0.016   #78  $4.00 Dellorto 40 (.0168), Bing 44 (.0167)
0.017   wire  $0.50 Dellorto 42 (.0177), Bing 46 (.0175)
0.018   #77  $3.50 Dellorto 44 (.0186), Bing 50 (.0188)
0.019   ——  $2.00 Dellorto 46 (.0194), Bing 52 (.0194)
0.0197 0.50  $2.00 Dellorto 48 (.0202), Bing 54 (.0200), “Metric” 51 (.0201)
0.0200 #76  $3.50 Dellorto 49 (.0207), Bing 56 (.0206), Gurtner 210=52 (.0210)
0.021   #75  $4.00 Dellorto 51 (.0215), Bing 58 (.0213), Gurtner 220=54 (.0220)
0.0225 #74  $5.00 Dellorto 55 (.0231), Bing 62 (.0229), Gurtner 230=56 (.0230)
0.023   ——  $2.00 Dellorto 56 (.0235), Bing 64 (.0234), Gurtner 240=58 (.0236)
0.0235 0.60  $2.00 Dellorto 58 (.0242), Bing 66 (.0239), Gurtner 245=59 (.0239)
0.0235 0.60  $1.50 Dellorto 58 (.0242), Bing 66 (.0239), Gurtner 250=60 (.0242)
0.024   #73  $3.00 Dellorto 60 (.0247), Bing 68 (.0248), “Metric” 63 (.0248)
0.025   #72  $3.50 Dellorto 62 (.0255), Bing 70 (.0254), “Metric” 65 (.0256)
0.026   #71  $4.50 Dellorto 66 (.0268), Bing 74 (.0267), “Metric” 68 (.0268)
0.0275 0.70 x N/A  Dellorto 70 (.0280), Bing 78 (.0280), “Metric” 71 (.0280)
0.028   #70  $4.00 Dellorto 72 (.0287), Bing 80 (.0287), “Metric” 73 (.0287)
0.0292 #69  $4.50 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  $4.50 Dellorto 82 (.0318), “Metric” 81 (.0319)
0.0315 0.80  $2.00 Dellorto 84 (.0324), “Metric” 82 (.0323)
0.032   #67  $3.00 Dellorto 86 (.0331), “Metric” 84 (.0331)
0.0325  —— $2.00 Dellorto 88 (.0337), “Metric” 86 (.0339)
0.033   #66  $4.50 Dellorto 90 (.0343), “Metric” 88 (.0346)
0.034   wire     N/A “Metric” 90 (.0354)
0.035   #65  $3.00 “Metric” 92 (.0362), Gurtner MB (side mount) diffuser (.0358)
0.0354 0.90  $2.00 “Metric” 94 (.0370)
0.036   #64  $3.00
0.037   #63  $2.50
0.038   #62  $1.50
0.039   #61  $1.50
0.0394 1.00  $1.00

 


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 $3-$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.

 

 

 

Here is a pin vise, a mini drill chuck, price $8

 

 

 

 

 

 

 


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).