Keihin Carburetors

January 3, 2015

Contents

01. Welcome  carb ID  xxxx  year range  US / Euro model xxxxxxxx (speed, engine)

02. Keihin 50A, 50Bparts for  1964-68 Honda P50 xxxxxxxxxxxx  (40km/h OHC)
02. Keihin 610 (50B) parts for  1967-68 Honda P50 Little Honda     (26 mph OHC)
03. Keihin C4B, C5B  parts for  1969-70 Honda PC50A (t 2039)  (40,50km/h OHC)
03
. Keihin C5A, C5A  parts for  1969-70 Honda PC50 Little Honda   (26 mph OHC)
03. Keihin F4A, F5A  parts for  1970-74 Honda PC50K1
xxxxxx  (40,50km/h OHV)
03. Keihin F4A, F4A  parts and 1970-74 Honda PF50 Amigo
xx   (40,50km/h OHV)
04. Keihin PA 01A-A, PA 00A-A 1975-77 Honda PC50K1 xxxxxx  (40,50km/h OHV)

04. Keihin PA 01A-A  parts and 1975-78 Honda PF50R Amigo x   (40,50km/h OHV)

04. Keihin PA M0A-A parts for  1978-80
Indian AMI50 4-Stroke xx   (30 mph OHV)
0
5. Keihin BB
21A-B  parts for  1978-79 Honda PA50-I Hobbit xxx   (20 mph TS)
05. Keihin BB
20A-C  parts for  1978-83 Honda PA50-II Hobbit xx    (30 mph TS)
0
6. Keihin PA 08B-A  parts for  1977-79 Honda NC50 Express xxx   (30 mph TS)
56. Keihin PA 08B-B  parts for  1977-79 Honda NC50 Express xxx  
(30 mph TS)
05. Keihin PA 08B-A  parts and 1979-79 Honda NA50 Express II xx  (30 mph TS)
0
7. Keihin PA 08E-A  parts for  1980-80 Honda NC50 Express xxx   (30 mph TS)
06. Keihin PA 08D-A  parts for  1980-80 Honda NA50 Express II xx  (30 mph TS)
0
8. Keihin PA 15A-A  parts for  1981-81 Honda NC50 Express xxx   (30 mph TS)
07. Keihin PA 16A-A  parts for  1981-81 Honda NA50 Express II xx  (30 mph TS)
0
9. Keihin PA 13E-A  parts for  1981-82 Honda NX50 Express SR x  (30 mph TS)
08. Keihin PA 13E-A  parts and 1982-83 Honda NC50 Express xxx   (30 mph TS)
08. Keihin PA 13E-A  parts and 1982-83 Honda NU50 Urban Express(30mph TS)
10. Keihin PA 29C-D  parts for  1984-87 Honda NQ50 Spree xxxxx  (30 mph TS)
09. Keihin PA 13E-A  parts and 1983-85 Honda NB50 Aero 50 xxx   (30 mph TS)

– – – – – – – – – < p a r t i t i o n > – – – – – – – – –
11. Keihin PA  Z502  parts for  1968-71 Honda Z50A Mini Trail
12. Keihin PA 655-A  parts for  1972-75 Honda Z50A Mini Trail
12. Keihin PA 674-A  parts for  1970-75 Honda QA50
13. Keihin PA 03A-A  parts for  1976-78 Honda Z50A Mini Trail
14. Keihin PA 03B-A  parts for  1979-81 Honda Z50R
14. Keihin PA 03C-A  parts for  1980-81 Honda Z50R
12. Keihin PA 03D-A parts  for  1982-85 Honda Z50R
12. Keihin PA 03D-A  parts for  1986-87 Honda Z50R
15. Keihin PA 03H-B  parts for  1988-91 Honda Z50R
15. Keihin PA 03M-A  parts for  1992-99 Honda Z50R
16. Keihin PA 42A-C  parts for  2000-03 Honda XR50R
16. Keihin PA 42A-C  parts for  2004-09 Honda CRF50F
17. Keihin carburetor parts for many small Hondas  

18. Gasket and O-Ring Replacement Sets

 

Keihin


1. Welcome

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 introduction 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.

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 (made in Belgium) carburetor, which is a unique design, these Honda moped, noped, mini-cycle, scooter and small motorcycle carbs are all model code “PA”. Other Keihin carburetor model codes are PB, PC, PD, PJ, PWK, CV, CVK, VB, VD, VE.

 


2. Keihin 50A, 50B on #044 1964-68 Honda P50 Little Honda

1964 P50 (NL model)

1967 Honda P50

1968 P50 (US model)

Bore:  42.0mm
Stroke 35.6mm
Displacement: 49cc

 

 

 

 

Honda P50 carburetors, top 50A, bottom 50B

These are down-draft carburetors, unusual, like the wheel-motor design is.

Top: Type 50A Carburetor 1964-67
(before frame number A148608)
Keihin ???, Honda 16100-
044-405
Main Jet: 55
Idle Jet: 35
Needle Jet: 2.6 x 2.0

Bottom: Type 50B Carburetor 1967-68
(after frame number A148607)
Keihin 610, Honda 16100-???-???
Main Jet: 62
Idle Jet: 35
Needle Jet: 2.6 x 1.55

 

 

 

 

 

 

 

 

 

 

 

 

 


3. Keihin (9mm) 0 C4B on #063 1969-70 Honda PC50A,K (40km/h)
3. Keihin (10mm)  C5B on #063 1969-70 Honda PC50A,K (50km/h)
3. Keihin (9mm) 0 C5A on #063 1969-70 Honda PC50 Little Honda
3. Keihin (9mm) o F4A on #063 1970-74 Honda PC50K1, PF50 (40km/h)
3. Keihin (10mm)  F5A on #063 1970-74 Honda PC50K1, PF50 (50km/h)

1969-70 Honda PC50 (USA)

1969-70 Honda PC50 (USA)

1969 Honda PC50A (Euro)

Bore:  42.0mm
Stroke 35.6mm
Displacement: 49cc

 

 

 

 

1969 Honda PC50 carburetor illustration

1969-70 Honda PC50

1973 Honda PC50K1

Before April 1970, the PC50 had a OHC engine (over head cam). The C4B, C5A, C5B carburetors for the early 1969-70 PC50A were spigot mount type, 16100-063-004. They had a round float bowl gasket (with three flat sides when installed), a long push-in jet, jet pad, completely round “donut” float, all metal float needle with replaceable float seat.

After April 1970, the PC50 had a OHV engine (over head valve) with pushrods instead of a cam chain.  The F4A, F5A, carburetors for the 1970-74 PC50K1 were flange mount type, but everything else was the same, round float bowl gasket (with three flat sides when installed), a long push-in jet, jet pad, completely round “donut” float, all metal float needle with replaceable float seat.

Honda early PC50 carburetor

Keihin C5A carb, spigot mount.

Carburetor: 9mm (C4B up to 2039616)
Carburetor: 10mm (C5B after 2039616)
Main Jet:
55 (C4B, C5A), 62 (C5B)
Idle Jet: 35
Needle Jet: 2.1 x 2.5
Float Needle: all metal 16123-063-004

 

 

 

 

 

 

Keihin F4A carb, flange mount

Carburetor: 9mm (F4A) (1970-74)
Carburetor: 10mm (F5A) (1970-74)
Main Jet:
55 (F4A), 62 (F5A)

Idle Jet: 35
Needle Jet: 2.1 x 2.5
Float Needle: all metal 16123-063-004
Flange Mount: 32mm hole spacing,
2 x 18 (22 od) o-ring, goes in pipe not carb

 

 

The 1970-74 Honda PC50K1 carburetor is illustrated below. The illustration there belongs here. But that is where it came from. 

 


4. Keihin 0(9mm) PA 01A on 1975-77 Honda PC50K1 000 (40 km/h)
4. Keihin 0(9mm) PA 01 and 1975-78 Honda PF50 Amigo (40 km/h)
4. Keihin (10mm) PA 00A on 1975-77 Honda PC50K1 000 (50 km/h)
4. Keihin (10mm) PA 00 and 1975-78 Honda PF50 Amigo (50 km/h)
4. Keihin (10mm) PA M0A on 1978-80 Indian AMI50 oo o (30 mph)

Late PC50: The carburetor changed from “donut” float to a swinging float, and a NC50-type float bowl and gasket. The 1975-77 PC50K1 and 1975-78 PF50 engine and carb are the same as the Taiwan remake engine and Keihin carburetor used on the 1978-80 Indian moped. So the carburetor parts are the same also, with a couple of exceptions.

PA 00A (16100-081-024) and PA 01A (16100-099-693) have the same parts. The jet size and venturi size are the only difference.

PA M0A has the same parts, but has a screw-in jet, size 70, M6-0.75 thread

Flange Mount: 32mm hole spacing, 2 x 18 (22 od) o-ring

Honda PC50 late carb

1975-77 PC50 carb

1973-74 late PC50 carburetor Keihin PA00A

Late PC50 carburetor
Keihin PA 00A-A

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

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

PA 00A-A gasket set $23

 

 

 

 

 

 

 

 

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

1980 Indian AMI-50

Indian AMI50: The Indian AMI50 Chief four stroke moped engine, OHV with pushrods and internal pedals, made from 1978-1984, is a Taiwan-made copy of a “late” Honda PC50 engine, OHV with pushrods and internal pedals, made from 1975-1978.

The Indian moped had three different carburetors, Tillotson (some 1978), Keihin (some 1978, most 1979-80), Mikuni (some 1980, all 1981-84). Only the Keihin parts are listed here. See Indian Parts for Mikuni items.

The Keihin carb on Indian is the same as late PC50, except for the jet, jet pad, jet o-ring, and float bowl. The mount holes are also 32mm spacing, center-to-center.

1978-80 Indian AMI50 with Keihin PA M0A-A

1975-77 Honda PC50 with Keihin PA 00A-A

 

 

 

 

 

 

 

 

 

 

 

Keihin (Indian) carburetor illustration

1970-74 PC50 carb illustration
from 1978-80 Indian parts catalog
4, 8, 15, 17 are different on Indian

Most of these PA MOA parts are the same as in PA 08B section 6.
Scroll down to those item numbers to see the prices there.  

cxx  price x Indian part #  Honda part #x description xxx specs
0
see6- N/A  E210-20-50 00000-000-000 PA M0A-A carb complete
02  see 6-5.0a E231-03-00 00000-000-000 substitute cap brass M20-1.0 thread
2a  see 6-1.1a E231-00-00 00000-000-000 top rubber washer 10 x 18 x 1
03  see6-0$3  E231-00-00 00000-000-000 cable stop-adjuster M6-0.75 thread
04  see 6-4.1b E231-06-00 16013-147-004 float white plastic non-stirrup type
05  see 6-2.0b E231-13-00 16155-883-005 float needle valve non-stirrup type
06  see 6-4.2x E231-15-00 00000-000-000 hinge pin substitute Ø2 x 18.5
07  see 6-11.0 E231-04-00 00000-000-000 rubber boot substitute Dellorto
08  see6-$40  E231-01-00 16015-081-004 float bowl like 08B-A but no jet pad
09  see 6-8.1x E231-07-00 16022-143-620 throttle slide Ø13 #15A 
10  see 6-3.3x E231-09-00 00000-000-000 jet needle D348 thick Ø2 x 33
11  see 6-3.1x E231-08-00 00000-000-000 W-spring clip
12  see 6-3.2x E231-10-00 00000-000-000 needle E-clip substitute 1.5mm
13  see 6-7.3x E231-19-00 00000-000-000 idle air mix screw M6-0.75 special
14  see 6-7.1x E231-21-00 00000-000-000 idle speed screw M4-0.70 special
15  see 6-6.1x E231-23-00 00000-000-000 bowl drain screw M6-1.00 special
17  see 6-1.5x E231-02-00 00000-000-000 float bowl gasket Ø1.5 NC50-type
19  see 6-7.4x E231-20-00 00000-000-000 idle air screw spring Ø5.6 x 10
20  see 6-7.2x E231-22-00 00000-000-000 idle speed screw spring Ø4.9 x 9
21  see 6-8.2x E231-17-00 00000-000-000 throttle return spring Ø10 x 42
22  see 6-1.6x E231-11-00 00000-000-000 drain screw o-ring 1.5×4 (7 od)
23  see6-0$2  E231-11-00 00000-000-000 intake flange o-ring 2 x 18 (22 od)
24  see6- N/A  E210-00-50 00000-000-000 carb body bare
27  see 8-19.0 E231-18-00 99101-187-070 screw-in main jet #70 M6-0.75 slot
28  see 6-4.3x E231-16-00 00000-000-000 hinge pin screw M4 x 6 sunk
29  see 6-12.0 E231-00-00 00000-000-000 bowl screw M4 x 10 pan phillips

PA M0A-A gasket set $18

Float Bowl: This Keihin carburetor illustration from the Indian Parts Manual shows a round bowl gasket, a round detached float, and a different float bowl. But the actual Indian carburetor has a #17 an NC50-type bowl gasket, #4 a swinging semi-round float, and #8 a Z50-type float bowl that is different from both NC50 type A shallow and NC50 type B deep float bowls.

 

 

 


5. Keihin (10mm) BB 21A-B  #148 on 1978-79 Honda PA50 I  Hobbit (20 mph)
5. Keihin (12mm) BB 20A-C  #148 on 1978-80 Honda PA50 II Hobbit (30 mph)
5. Keihin (12mm) BB 20A-C  #GB7 on 1981-83 Honda PA50 II Hobbit (30 mph)

1978 Honda PA50II 30mph

1978 Honda PA50II

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 Belgium by Honda Benelux, so it had a mix of Japanese and European design and componentry. 

In US models, 20mph versions were 1978-79 red. 30mph versions were 1978-79 yellow, 1980 yellow, 1981-82 red, and 1983 black.

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. It has to be special because it swings up and down with the engine, and is very close to the frame at the place where you step through.   

Keihin (1978-83 Honda PA50) carburetor illustration

1978-83 Honda PA50 carb

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23

 

 

 

 

 

 

 

 

1978 PA50 carb service

PA50 carb removal

 

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.

 


6. Keihin (12mm) PA08B-A or PA08B-B  on #147 1977-79 Honda NC50 Express
6. Keihin (12mm) PA08B-A or PA08B-B  on #163 1979 Honda NA50 Express II

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. The mount holes have a 38mm spacing, wider than the late PC50 flange mount baby Keihin.

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  
1.0a$22 16010-143-620 gasket set PA08B-A
1.0b$22 16010-147-711 gasket set PA08B-B
1.1a$$3 16010-143-305 top rubber washer 10 x 18 x 1
1.1b$$8 16010-143-305 top rubber washer 13 x 16.5 x 1
1.2x$$2 16010-143-305 intake o-ring 2 x 20 (24 od) 
1.3a$$2 16010-143-305 main jet o-ring 1 x 3 (5 od)
1.4a$$5 16010-143-305 jet support pad disk Ø7.5 x 1.8 
1.5x$15 16010-143-305 float bowl gasket  Ø1.5 NC50-type
1.6x$$2 16010-143-305 drain plug o-ring 1.5×4 (7 od)
2.0a$25 16011-881-741 float needle valve  stirrup (KL 18-4612)
2.0b$20 16155-883-005 float needle valve regular (KL 18-4608)
3.0a N/A 16012-147-004 needle jet and jet needle set PA 08B-A
3.0a $22 16012-130-640 needle jet and jet needle set PA 03A-A
3.0a $22 16012-165-014 needle jet and jet needle set PA 03B-A    

3.0b$15 16012-147-014 needle jet and jet needle set PA 08B-B
3.1x$$5 00000-000-000 jet needle w-clip
3.2x$$2 00000-000-000 jet needle e-clip 1.5 for Ø2.0 needle
3.3x$10 00000-000-000 jet needle Ø2.0 D348 thick PA 08B-A,
3.3x$10 PA 08B-B, PA 03A-A, PA 00A-A, PA 01A-A

3.3x$10 00000-000-000 jet needle Ø2.0 D117 thin PA 03B-A,
3.3x$10 PA 03C-A, PA 03D-A, PA 03H-B, PA 03M-A, etc
3.4a N/A 00000-000-000 needle jet (emulsion tube) PA 08B-A

3.4a $10 00000-000-000 needle jet (emulsion tube) PA 03A-A
3.4a $10 00000-000-000 needle jet (emulsion tube) PA 03B-A

4.0a N/A 16013-143-620 float with pin and screw, black stirrup
4.0b N/A 16013-147-004 float with pin and screw, white regular
4.1a N/A 00000-000-000 float bare, solid black foam stirrup
4.1b N/A 00000-000-000 float bare hollow white plastic regular
4.2x$$4 00000-000-000 hinge pin substitute Ø2 x 18.5
4.3x$$3 00000-000-000 hinge screw M4x5 sunk phillips
5.0a$25 16014-143-620 top cap A and washer subst. M20-1.0
5.0b$22 16014-147-004 top cap B and washer subst. M18-1.0
6.0a see below 16015-147-004 chamber set A shallow with pad
6.0b see below 16015-GA6-681 chamber set B deep, no jet pad
6.1x$16 00000-000-000 float drain screw M6x20 special
7.0x$15 16016-143-620 adjustment screw set
7.1x$$4 00000-000-000 idle speed screw M4x19 special
7.2x$$2 00000-000-000 idle speed screw spring Ø5.6 x 10
7.3x$$6 00000-000-000 idle air screw M6-0.75×20 special
7.4x$$5 00000-000-000 idle air screw spring Ø4.8 x 9
8.0x$38 16022-143-620 throttle slide and spring
8.1x$25 00000-000-000 throttle slide Ø13 #15A
8.2x$15 00000-000-000 throttle spring original Ø9.5 x 42
8.3x$$5 00000-000-000 throttle spring substitute shorter, stiffer

9.0x$25 16046-143-620 choke top, spring, slide substitute
9.1x$10 00000-000-000 choke top substitute plastic M12-1.0
9.1x$15 00000-000-000 choke top substitute metal M12-1.0
9.2x$$4 00000-000-000 choke spring substitute
9.3x$12 00000-000-000 choke slide substitute
10a  N/A 16100-147-712 carburetor assy. 1977-79 PA 08B-A
10b  N/A 16100-147-676 carburetor assy. 1978-80 PA 08B-B

PA 08B-B gaskets $22

PA 08B-A gaskets $22

11.0x $5 16118-166-004 cable rubber boot substitute Dellorto
12.0x $1 93500 – 04012 bowl screw M4x12 pan phillips
13.0 25¢ 94111 – 04000 lock washer M4 split
14.0xN/A 95001 – 35003 drain and overflow hose 3.5 x 7.0
14.0x $1 95001 – 35003 drain hose subst. 1/8 x 1/4 3.1 x 6.3
15.0xN/A 95002 – 02070 drain hose clamp B7 (for 7 not 6.3)
16.58$12 99201-081-0580 jet push-in 58 (58 drilled) PA 03A-A
16.70$18 99201-081-0700 jet push-in 70 (58 drilled) PA 00A-A

16.78$18 99201-081-0780 jet push-in 78 (58 drilled) PA 08B-A
16.0bN/A non-replaceable main jet, part of carb body  PA 08B-B

 

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 top plastic 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.

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 (12mm) PA08E-A on #147 1980 Honda NC50 Express
7. Keihin (12mm) PA08D-A on #163 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.

PA 08E-A gasket set $27

PA 08D-A gasket set $22

 

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)

8. Keihin (12mm) PA15A-A on #163 1981 Honda NC50 Express
8. Keihin (12mm) PA16A-A on #190 1981 Honda NA50 Express II

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. They both have a #75 screw-in jet and the non-stirrup type B float needle. The only difference must be the venturi shape or size.

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
1.0  see 6 $27 16010-190-004 gasket and o-ring set
1.1  see 6-1.1b 16010-143-305 top rubber washer 13 x 16.5 x 1
1.2  see 6-1.2x 16010-143-305 intake o-ring 2 x 20 (24 od) 
1.3  see 6-$22 16010-143-305 float bowl gasket 2.5 tall by 1.5 wide
1.4  see 6-1.6x 16010-143-305 drain plug o-ring 1.5 x 4 (7 od)
1.5  see 6-1.3a 16010-143-305 idle fuel mix screw o-ring 1 x 3 (5 od)
2.0  see 6- N/A 16012-GA6-671 needle jet & jet needle set PA15A-A
2.1  see 6-3.1x 00000-000-000 jet needle w-clip
2.2  see 6-3.2x 00000-000-000 jet needle e-clip for 1.5 clip groove
2.3  see 6-3.3x 00000-000-000 jet needle D348 thick 2.0 x 33
2.4  see 6- N/A 00000-000-000 needle jet (emulsion tube) PA15A-A
3.0  see 6-4.0b 16013-147-004 float set white plastic regular
3.1  see 6-4.1b 00000-000-000 float bare white plastic
3.2  see 6-4.2x 00000-000-000 hinge pin substitute Ø2 x 18.5
3.3  see 6-4.3x 00000-000-000 hinge screw M4x5 sunk phillips
4.0  see 6- N/A 16014-190-014 top cap with curved pipe 1981
4.0  see 6- N/A 16014-187-013 top cap with curved pipe 1982-83
5.0  see 6-6.0b 16015-GA6-671 float bowl set deep bowl with choke jet
5.1  see 6-6.1x 00000-000-000 float drain screw M6 x 20 special
6.0  see 6- $22 16016-191-004 idle fuel adjustment screw set
6.1  see 6- $15 00000-000-000 idle fuel mixture screw M6-0.75 special
6.2  see 6-7.4x 00000-000-000 idle fuel mix screw spring Ø5 x 9
6.3  see 6-  $2 00000-000-000 idle fuel mix screw washer 3.1×5.0x0.5
7.0  see 6-8.0 16022-143-620 throttle slide & spring
7.1  see 6-8.1x 00000-000-000 throttle slide Ø13 #15A
7.2  see 6-8.2x 00000-000-000 throttle slide spring Ø9.5 x 42
8.0  see 6-7.0 16028-187-003 idle speed screw and spring
8.1  see 6-7.1x 00000-000-000 idle speed screw M4x19 special
8.2  see 6-7.2x 00000-000-000 idle speed screw spring Ø5.5×10
9.0  see 6-N/A 16100-190-672 carburetor assembly 1981
9.0  see 6-N/A 16100-GA6-671 carburetor assembly 1982-83
10  see 6- N/A 16118-190-004 cable curved rubber boot (1981)

10  see 6- N/A 16118-187-003 cable curved rubber boot (82-83)
11  see 6-2.0b 16155-883-005 float needle valve (KL 18-4608)
12  see 6-14.0 16199-435-771 float drain hose 3.0 x 6.5
13  see 6- N/A 16608-GA6-670 control valve tube 4
14  see 6-12.0 93892-04012-08 screw & washer M4x12 pan phillips
15  see 6-15.0 95002 – 02070   hose clamp B7 for vent hose
16  see 6- N/A 95002 – 02080   hose clamp B8 for vacuum hose
17  see 6- N/A 95002 – 02650   hose clamp B6.5 for drain hose
18
 see 6-14.0 95005 – 35001   float vent hose 3.5 x 7
19  see 6- N/A 99101-187-0580 screw-in jets M6-0.75 thread:
19  see 6- N/A 99101-187-0580 jet #58 (82-87 Z50R)

19  see 6- N/A 99101-187-0680 jet #68 (84-87 Spree)
19  see 6- $$7 99101-187-0700 jet #70 (78-80 Indian)
19  see 6- N/A 99101-187-0750 jet #75 (81-83 Express)

19  see 6- $$7 99101-187-0760 jet #76
19  see 6- $$7 99101-187-0780 jet #78 (KL 18-9792) 
19  see 6- N/A 99101-187-0800 jet #80 (KL 18-9793) 

PA15A-A gaskets $27

Keihin late NC50 adjustment screws

1980-83 NC50 idle adjustment screws
8.1 idle speed screw, tighter is faster idle
6.1 idle fuel mix screw, tighter is 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. 

Choke jet: On 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.  

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

 

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

 

 


9. Keihin (12mm) PA13E-A  on #187 1981-82 Honda NX50 Express SR
9. Keihin (12mm) PA13E-A  on #GA6 1982-83 Honda NC50 Express
9. Keihin (12mm) PA13E-A  on #GC1 1982-83 Honda NU50 Urban Express

Keihin PA13E-A carb Honda NX50

Keihin PA13E-A 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 Honda NU50 Urban Express

1982 NU50 Urban Express

 

 

 

 

 

 

 

1982 Honda NX50 Express SR

1982 NX50 Express SR

1982-83 NC50 hoses

1982-83 Honda NC50, NU50 hoses explained

 

 

 

 

 

 

PA13,15,16 gaskets $27

 

 

 

 

 

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.

 

 


10. Keihin PA 29C-D, PA29H-A, others on #GK8 1984-85 Honda NQ50 Spree
10. Keihin PA 29C-D, PA29H-A, others on #GE8,GN2 1983-85 Honda NM50 Aero 50

Keihin (1985-87 Honda NM50) carburetor illustration

The gasket is drawn wrong

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 50

1985 Honda NQ50 Spree

1985 Honda NQ50 Spree

 

 

 

 

 

 

 

 

Spree carburetor PA 29C-D exposed

PA 29C-D gaskets N/A

 

 

 

 

 

 

 

 

The float bowl gasket in the illustration looks like the NC50-type, but it’s not. The actual gasket has an additional loop, for a vent and overflow. A “tall” float bowl gasket for a 1982-83 NC50 would work fine. Only if the float overflowed then some of the overflow would leak onto the carb instead of through the overflow hose and onto the ground.

From measuring an actual PA 29C-D carburetor, the sizes can be displayed in the PA 29C-D gaskets photo. The PA 29C-D gasket set is not available but the PA15A-A gasket set can be a substitute. See above.

Idle Mixture Screw: The idle mixture screw is an “air screw” that blocks off an air channel.

Main Jet: The main jet is a screw-in, recessed-type, M6-0.75 thread, size 68 (0.68mm).

Pilot Jet: The idle jet is not replaceable. It is inside the upper end of the brass tube, pressed into the main body, on the engine side of the main jet.

Float Seat: This carb does not have a replaceable float needle valve seat. The seat is part of the main body, and must be cleaned and polished with a spinning Q-tip.

Float: non-stirrup type white plastic 16013-147-004 see 6-4.0b, non-stirrup needle valve 16155-883-005 see 6-2.0b

Flange Mount: The flange mount holes on the Spree carburetor are spaced 35mm, center-to-center. That is different from the late PC50 32mm, and the NC50 38mm, and Z50 32mm (1976-78 38mm)

Top Cap: M18 x 1 thread

 

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