Mikuni Cv Carburetor Manual

To avoid injury, carburetors should be installed when the engine is cold. Read the owners manual for your vehicle before installing any Keihin product to prevent any damage to the vehicle due to improper installation. Gasoline is extremely flammable and can be explosive under certain conditions. Mikuni BS (CV) Carburetor Rebuild Tutorial Use caution when removing float seat to assure brass seat is not crushed Inspect the float needle and seat carefully. The spring on the needle must be smooth and the tip free of wear (if you feel a ridge on the tapered portion of the needle it needs to be replaced).

TM SERIES FLAT SLIDE NEW STYLE EXPLODED VIEW

Other TM series parts in addition to what is listed below.
1. Complete Starter System, VM28-418 (TM28) VM26/116 002-815
1. Complete Starter System TM32-1, TM34-2, TM36-2, TM38-1 VM29/47 002-816
1. Complete Starter System TM38-3, TM38-85, TM38-86 VM29/47 002-816
1. Complete Starter System TM39 and TM41 Pro Series VM29/47 002-816
2. Nylon Ring TM24-8001 VM24/791A 002-780
2. Nylon Ring TM28, TM32-34 VM28/1046 002-754
2. Nylon Ring TM36-2, TM38-1, TM38-3, VM38/153 002-753
2. Nylon Ring TM38-85, TM38-86, TM39/41 Pro VM38/153 002-753
3. Screw with Lock Washer for Cable Connector TM24-8001 CW2=2608 007-265
3. Screw with Lock Washer for Cable Connector VM28-418 (TM28), TM32-1, TM34-2, CW2=0310 002-752
3. Screw with Lock Washer for Cable Connector TM36-2, TM38-1, TM38-3 CW2=0310 002-752
3. Screw with Lock Washer for Cable Connector TM38-85, TM38-86, TM39/TM41 Pro CW2=0310 002-752 CW2=0310 002-752
4. Cable Connector TM24-8001 VM24/790 002-758
4. Cable Connector TM36-2, TM38-85, TM38-86 VM38/152 002-751
4. Cable Connector TM39 and TM41 Pro Series VM38/152 002-751
5. E-Ring (Needle Clip) All TM Series VM20/369 002-083
6. NEEDLES
7. Throttle valves

TM24 (TM24-8001) 3.0 832-30005 002-951
TM28 (VM28-418) 2.5 832-33001 002-804
TM32 (TM32-1) 4.0 832-39012 (TM32-1 uses same as TM34-2) 002-800
TM34 (TM34-2) 4.0 832-39012 (TM32-1 uses same as TM34-2) 002-800

Old Style TM 36, TM38 Carburetor with Top Idle Adjuster Rod TM36 (TM 36-2), TM38 (TM38-1, TM38 (TM38-3)
2.5 832-43002 002-734
3.0 832-43002 002-735
4.0 832-43002 002-737
5.0 832-43002 002-739

New Style TM 38 Carburetor, with Side Idle Adjuster Screw TM38 (TM38-85), TM38 (TM38-86)
2.5 832-43011 007-401
3.0 832-43011 007-402
3.5 832-43011 007-403
4.0 832-43011 007-404
4.5 832-43011 007-405

8. Idle Rod (TM Carburetors with Top Idle Adjustment) TM36-2, TM38-1, TM38-3 VM38/159 002-732
10. Screw, Jet Block All TM Series VM38/132 002-742
11. Washer All TM Series VM34/274 002-741
12. Jet Block, Left - TM38-1, TM38-3 VM38/144 002-710
13. Jet Block, Right - TM38-1, TM38-3 VM38/145 002-711
14. Float Pin All TM Series BV26/22 002-107
15. Float Arm TM32-1, TM34-2, TM36-2, TM38-1 VM36/15 002-112
15. Float Arm TM38-3, TM38-85, TM38-86 VM36/15 002-112
15. Float Arm TM39 and TM41 Pro Series VM36/15 002-112
16. Cap, Float Guide Pin VM28-418 (TM28), TM32-1, TM34-2 VM26/42 002-718
16. Cap, Float Guide Pin TM36-2, TM38-1, TM38-3 VM26/42 002-718
17. Pilot Jet All TM Series VM22/210
18. Float TM24-8001 VM24/365 007-255
18. Float VM28-418 (TM28) VM28/694 007-726
18. Float TM32-1, TM34-2, TM36-2, TM38-1 VM24/236 002-113
18. Float TM38-3 VM24/236 002-113
18. Float TM38-85, TM38-86, TM39/41 Pro RH 859-52020 002-481
18. Float TM38-85, TM38-86, TM39/41 Pro LH 859-52021 002-482
19. Gasket, Float Chamber TM24-8001 VM20/492 007-250
19. Gasket, Float Chamber VM28-418 (TM28) VM26/228 007-251
19. GASKET, FLOAT CHAMBER TM32-1,TM34-2,TM36-2,TM38-1 VM34/374 002-700
19. GASKET, FLOAT CHAMBER TM38-3, TM38-85, TM38-86 VM34/374 002-700
19. GASKET, FLOAT CHAMBER TM39 and TM41 Pro Series VM34/374 002-700
20. Float Bowl Assembly TM36-2, TM38-1, TM38-3 TM32/02-100 002-701
20. Float Bowl Assembly TM38-85, TM38-86, TM39/41 Pro TM38/138 007-767
21. Plate, Hose Retaining VM28/79A 002-204
22. Screw with Lock Washer TM24-8001 CW2=0416-B 002-615
22. Screw with Lock Washer VM28-418 (TM28) CW2=0416 002-823
22. Screw with Lock Washer TM32-1, TM34-2, CW2=0516 002-373
22. Screw with Lock Washer TM36-2, TM38-1, TM38-3, TM38-85, TM38-86, TM39/41 Pro CW2=0518 002-719
22. Screw with Lock Washer TM38-85, TM38-86, TM39/41 Pro CW2=0518 002-719
23. O-Ring VM28-418 (TM28) VM26/227 002-825
23. O-Ring TM32-1, TM34-2, TM36-2, TM38-1 VM28/254 002-531
23. O-Ring TM38-3, TM38-85, TM38-86 VM28/254 002-531
23. O-Ring TM39 and TM41 Pro Series VM28/254 002-531
24. Drain Plug VM28-418 (TM28) VM28/817 002-827
24. Drain Plug TM32-1, TM34-2, TM36-2, TM38-1 VM28/253 002-526
24. Drain Plug TM38-3, TM38-85, TM38-86 VM28/253 002-526
24. Drain Plug TM39 and TM41 Pro Series VM28/253 002-526
25. Cap, Idle Adjuster TM36-2, TM38-1, TM38-3 VM35/40 002-731
26. Packing (Rubber) TM36-2, TM38-1, TM38-3 N138.077 002-730
27. Nut-TM36-2, TM38-1, TM38-3 N2=04 002-729
28. Idle Adjuster-TM36-2, TM38-1, TM38-3 603-68001 002-728
29. Nut-TM36-2, TM38-1, TM38-3 BDC36/35 002-727
30. Rubber Cap VM18/228 002-723
30. Rubber Cap TM24, VM28-418 (TM28) VM26/46 002-061
30. Rubber Cap TM32-1, TM34-2, TM36-2 VM18/228 002-723
30. Rubber Cap TM38-1, TM38-3 VM18/228 002-723
30. Rubber Cap TM38-85, TM38-86 VM34/282 002-452
31. Screw with Lock Washer All TM Series CW2=0412 002-748
32. Cable Adjuster VM28-418 (TM28) M18F/43A 002-062
32. Cable Adjuster TM32-1, TM34-2, TM36-2, TM38-1 VM36/83 002-724
32. Cable Adjuster TM38-3, TM38-85, TM38-86 VM36/83 002-724
32. Cable Adjuster TM39 and TM41 Pro Series VM36/83 002-724
33. Locknut VM28-418 (TM28) B30/247 002-065
33. Locknut TM32-1, TM34-2, TM36-2, TM38-1 B30/247 002-065
33. Locknut TM38-3, TM38-85, TM38-86 B30/247 002-065
33. Locknut TM39 and TM41 Pro Series B30/247 002-065
34. Mixing Chamber, Top TM24-8001 VM24/785 007-765
34. Mixing Chamber, Top TM36-2, TM38-1, TM38-3 776-19002 002-733
34. Mixing Chamber, Top TM38-85, TM38-86, TM39/41 Pro 776-19001 NA
35. Gasket, Top TM24-8001 VM24/785 007-765
35. Gasket, Top VM28-418 (TM28) VM28/1045 002-830
35. Gasket, Top TM32-1, TM34-2, VM32/495 007-268
35. Gasket, Top TM36-2, TM38-1, TM38-3 VM38/127 002-725
35. Gasket, Top TM38-85, TM38-86, TM39/41 Pro VM38/127 002-725
36. Spring, Throttle valve TM24-8001 730-11003 002-831
36. Spring, Throttle valve VM28-418 (TM28) 730-15021 002-832
36. Spring, Throttle valve TM32-1, TM34-2 730-15004 002-833
36. Spring, Throttle valve TM36-2, TM38-1, TM38-3, 730-16003 002-750
36. Spring, Throttle valve TM38-85, TM38-86, TM39/TM41 Pro 730-16003 002-750
37. Needle Jet TM24-8001 #454 Series Q-0 Needle Jet
37. Needle Jet VM28-418 (TM28) #175 Series P-8 Needle Jet
37. Needle Jet TM32-1, TM34-2, TM36-2 #389 Series Q-2 Needle Jet
37. Needle Jet TM38-1, TM38-3 #389 Series Q-2 Needle Jet
37. Needle Jet TM38-85, TM38-86, TM39/41 Pro #389 Series Q-2 Needle Jet
38. Ring, Main Jet TM24-8001 VM28/449 002-664
38. Ring, Main Jet VM28-418 (TM28) VM28/429 002-836
38. Ring, Main Jet TM32-1, TM34-2, TM36-2, TM38-1, TM38-3 VM34/454 002-837
38. Ring, Main Jet TM38-1, TM38-3 VM34/454 002-837
38. Ring, Main Jet TM38-85, TM38-86, TM39/41 Pro TM34/36 002-835
39. Main Jet All TM Series 4/042
40. O-Ring, Needle Valve TM24-28 VM24/559 002-838
40. O-Ring, Needle Valve TM32-41 KV10 002-709
41. Needle valve 1.5 WITH KV10 O-RING TM24-8001 STD MIKUNI# VM24/557A-1.5 (SKU 002-842)
41. Needle Valve 2.5 with KV10 O-Ring TM28, VM28-418 STD MIKUNI# VM24/557A-2.5 (SKU 002-840)
41. Needle valve 3.3 WITH KV10 O-RING TM32-1, TM34-2, TM36-2 STD MIKUNI# 786-46001-3.3 (SKU 002-705)
41. Needle valve WITH KV10 O-RING TM38-1, TM38-3 STD MIKUNI# 786-46001-3.5 (SKU 002-707)
41. Needle valve WITH KV10 O-RING TM38-85, TM38-86, TM39/41 PRO STD MIKUNI# 786-46001-3.5 (SKU 002-707)
42. Plate, Needle Valve All TM Series VM24/560 002-721
43. Screw All TM Series C2=0406 002-722
44. Vent Hose VM14/49 002-755
45. Gasket, Front Cover TM24-8001, VM28-418 (TM28) VM28/1044 002-847
45. Gasket, Front Cover TM38-85, TM38-86, TM39/41 Pro VM38/126 002-726
48. Screw All TM Series VM38/133 002-749
49. Air Screw, Pilot TM24-8001, VM28-418 (TM28) VM20/584 002-850
49. Air Screw, Pilot TM32-1, TM34-2, TM36-2, TM38-1 VM24/672 007-768
49. Air Screw, Pilot TM38-3, TM38-85, TM38-86 VM24/672 007-768
49. Air Screw, Pilot TM39 and TM41 Pro Series VM24/672 007-768
50. Spring, Pilot Air Screw All TM Series M12/46A 002-181
51. Washer, Pilot Air Screw TM32-1, TM34-2, TM36-2, TM38-1 VM12/33 002-856
51. Washer, Pilot Air Screw TM38-3, TM38-85, TM38-86 VM12/33 002-856
51. Washer, Pilot Air Screw TM39 and TM41 Pro Series VM12/33 002-856
52. O-Ring, Pilot Air Screw TM32-1, TM34-2, TM36-2, TM38-1 N133.037 002-858
52. O-Ring, Pilot Air Screw TM38-3, TM38-85, TM38-86 N133.037 002-858
52. O-Ring, Pilot Air Screw TM39 and TM41 Pro Series N133.037 002-858
53. Main Air Jet BS30/97
54. Overflow Hose VM14/49 002-755
55. Starter Jet All TM Series VM17/1002
56. Idle Stop Screw TM24-8001, VM28-418 (TM28) 603-27002 002-860
56. Idle Stop Screw TM32-1, TM34-2, TM38-85, TM38-86, TM39/41 Pro, TM39 and TM41 Pro Series 603-16003 002-861
56. Idle Stop Screw TM38-85, TM38-86, TM39/41 Pro 603-16003 002-861
56. Idle Stop Screw TM39 and TM41 Pro Series 603-16003 002-861
57. Spring, Idle Screw TM24-8001, VM28-418 (TM28) VM15/112 002-863
57. Spring, Idle Screw TM32-1, TM34-2 VM24/556 002-864
57. Spring, Idle Screw TM38-85, TM38-86, TM39/41 Pro VM24/556 002-864
58. O-Ring, Idle Screw TM24-8001, VM28-418 (TM28) VM14/75 002-676
58. O-Ring, Idle Screw TM32-1, TM34-2, TM38-85, TM38-86, TM39/41 Pro BV32/04 002-212
59. Washer TM24-8001, VM28-418 (TM28) VM14/87 002-866

007-731This adjuster has threads on one end, the other end swivels. Includes rubber cap, locknut, cable adjuster and 90ยบ tube. Works on Keihin and Mikuni carburetor caps.

The kit 007-731 contains:
002-061 rubber cap
002-065 nut
007-757 adjuster
007-759 90 degree threaded tube

TM POWER JET KIT

TM POWERJET KIT 002-041
The Power Jet Kit is used on 2-stroke engine applications to improve mid-range throttle response and add additional fuel to wide open throttle running conditions. Easily installs on TM series Carburetors (#80, #100 and #120 sized jets included). Sold as a kit.

TM Cable Type Starter System Kit. Replaces knob plunger type starter system with a cable type starter
system. Sold as a kit. Two Kits available:

Order No. 002-351
Fits the following TM Carburetors: TM32, TM34, TM36, TM38
and 39mm Pro-Series, 41mm Pro-Series
Includes items A - F.

Order No. 002-353
Fits the following TM carburetor: VM28/418 (TM28)
Includes items A - F.

A. Starter Plunger Top, Rubber Cap VM26/46 002-061
B. Cable Adjuster M21/14 002-062
C. Cable Adjuster Locknut B30/247 002-065
D. Starter Plunger Fitting VM15/37 002-093
E. Starter Plunger Spring VM32/69 002-094
F. Starter Plunger (TM32-TM41) VM15SC4/85 002-095
Starter Plunger (TM28) VM15SC4/86 007-751

TM Series Throttle valves

TM24 (TM24-8001) 3.0 832-30005 002-951
TM28 (VM28-418) 2.5 832-33001 002-804
TM32 (TM32-1) 4.0 832-39012 002-800
TM34 (TM34-2) 4.0 832-39012 002-800

Old Style TM 36, TM38 Carburetor with Top Idle Adjuster Rod
TM36 (TM 36-2), TM38 (TM38-1, TM38 (TM38-3)
2.5 832-43002 002-734 No longer available
3.0 832-43002 002-735 No longer available
4.0 832-43002 002-737
5.0 832-43002 002-739 No longer available

New Style TM 38 Carburetor, with Side Idle Adjuster Screw
TM38 (TM38-85), TM38 (TM38-86)
2.5 832-43011 007-401
3.0 832-43011 007-402
3.5 832-43011 007-403
4.0 832-43011 007-404
4.5 832-43011 007-405

TM33 Pumper (TM33-8012) 1.5 832-38007 002-948
TM40 (HS40) Pumper (TM40-6) TM40/81 007-430


NEEDLES

Mikuni Motorcycle Carburetor Theory 101

Motorcycle carburetors look very complex, but with a little theory, you can tune your bike for maximum performance. All carburetors work under the basic principle of atmospheric pressure. Atmospheric pressure is a powerful force which exerts pressure on everything. It varies slightly but is generally considered to be 15 pounds per square inch (PSI). This means that atmospheric pressure is pressing on everything at 15 PSI. By varying the atmospheric pressure inside the engine and carburetor, we can change the pressure and make fuel and air flow.

Atmospheric pressure will force high pressure to low pressure. As the piston on a two stroke engine goes up (or goes down on a four stroke engine), a low pressure is formed inside the crankcase (above the piston on a four stroke). This low pressure also causes a low pressure inside the carburetor. Since the pressure is higher outside the engine and carburetor, air will rush inside the carburetor and engine until the pressure is equalized. The moving air going through the carburetor will pick up fuel and mix with the air.

Inside a carburetor is a venturi, fig 1. The venturi is a restriction inside the carburetor that forces air to speed up to get through. A river that suddenly narrows can be used to illustrate what happens inside a carb. The water in the river speeds up as it gets near the narrowed shores and will get faster if the river narrows even more. The same thing happens inside the carburetor. The air that is speeding up will cause atmospheric pressure to drop inside the carburetor. The faster the air moves, the lower the pressure inside the carburetor.

FIG 1

Most motorcycle carburetor circuits are governed by throttle position and not by engine speed.There are five main metering systems inside most motorcycle carburetors. These metering circuits overlap each other and they are:
* pilot circuit
* throttle valve
* needle jet and jet needle
* main jet
* choke circuit

The pilot circuit has two adjustable parts, fig 2. The pilot air screw and pilot jet. The air screw can be located either near the back side of the carburetor or near the front of the carburetor. If the screw is located near the back, it regulates how much air enters the circuit. If the screw is turned in, it reduces the amount of air and richens the mixture. If it is turned out, it opens the passage more and allows more air into the circuit which results in a lean mixture. If the screw is located near the front, it regulated fuel. The mixture will be leaner if it is screwed in and richer if screwed out. If the air screw has to be turned more than 2 turns out for best idling, the next smaller size pilot jet will be needed.

FIG 2

The pilot jet is the part which supplies most of the fuel at low throttle openings. It has a small hole in it which restricts fuel flow though it. Both the pilot air screw and pilot jet affects carburetion from idle to around 1/4 throttle.

The slide valve affects carburetion between 1/8 thru 1/2 throttle. It especially affects it between 1/8 and 1/4 and has a lesser affect up to 1/2. The slides come in various sizes and the size is determined by how much is cutaway from the backside of it, fig 3. The larger the cutaway, the leaner the mixture (since more air is allowed through it) and the smaller the cutaway, the richer the mixture will be. Throttle valves have numbers on them that explains how much the cutaway is. If there is a 3 stamped into the slide, it has a 3.0mm cutaway, while a 1 will have a 1.0mm cutaway (which will be richer than a 3).

FIG 3

The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle. The jet needle is a long tapered rod that controls how much fuel can be drawn into the carburetor venturi. The thinner the taper, the richer the mixture. The thicker the taper, the leaner the mixture since the thicker taper will not allow as much fuel into the venturi as a leaner one. The tapers are designed very precisely to give different mixtures at different throttle openings. Jet needles have grooves cut into the top. A clip goes into one of these grooves and holds it from falling or moving from the slide. The clip position can be changed to make an engine run richer or leaner, fig 4. If the engine needs to run leaner, the clip would be moved higher. This will drop the needle farther down into the needle jet and cause less fuel to flow past it. If the clip is lowered, the jet needle is raised and the mixture will be richer.

The needle jet is where the jet needle slides into. Depending on the inside diameter of the needle jet, it will affect the jet needle. The needle jet and jet needle work together to control the fuel flow between the 1/8 thru 3/4 range. Most of the tuning for this range is done to the jet needle, and not the needle jet.

Mikuni Cv Carburetor Manual

FIG 4

The main jet controls fuel flow from 3/4 thru full throttle, fig 5. Once the throttle is opened far enough, the jet needle is pulled high enough out of the needle jet and the size of the hole in the main jet begins to regulate fuel flow. Main jets have different size holes in them and the bigger the hole, the more fuel that will flow (and the richer the mixture). The higher the number on the main jet, the more fuel that can flow through it and the richer the mixture.

Mikuni Carburetor Rebuild Instructions

FIG 5

The choke system is used to start cold engines. Since the fuel in a cold engine is sticking to the cylinder walls due to condensation, the mixture is too lean for the engine to start. The choke system will add fuel to the engine to compensate for the fuel that is stuck to the cylinder walls. Once the engine is warmed up, condensation is not a problem, and the choke is not needed.

The air/fuel mixture must be changes to meet the demands of the needs of the engine. The ideal air/fuel ratio is 14.7 grams of air to 1 gram of fuel. This ideal ratio is only achieved for a very short period while the engine is running. Due to the incomplete vaporization of fuel at slow speeds or the additional fuel required at high speeds, the actual operational air/fuel ratio is usually richer. Figure 6 shows the actual air/fuel ratio for any given throttle opening.

FIG 6

Carburetor Jetting Troubleshooting

Carburetor troubleshooting is simple once the basic principles are known. The first step is to find where the engine is running poorly, fig 7. It must be remembered that carburetor jetting is determined by the throttle position, not engine speed. If the engine is having troubles at low rpm (idle to 1/4 throttle), the pilot system or slide valve is the likely problem. If the engine has problems between 1/4 and 3/4 throttle, the jet needle and needle jet (most likely the jet needle) is likely the problem. If the engine is running poorly at 3/4 to full throttle, the main jet is the likely problem.

FIG 7

While jetting carburetors, place a piece of tape on the throttle housing. Place another piece of tape on the throttle grip and draw a line (while the throttle is at idle) straight across from one piece of tape to the other. When these two lines are lined up, the engine will be idling. Now open the throttle to full throttle and draw another line directly across from it on the throttle housing. At this point, there should be two lines on the throttle housing, and one on the throttle grip. Now find the half-way point between both of the lines on the throttle housing. Make a mark and this will show when the throttle is at half throttle. Divide the spaces up even again until idle, 1/4, 1/2, 3/4, and full throttle positions are known. These lines will be used to quickly find the exact throttle opening while jetting.

Clean the air filter and warm the bike up. Accelerate through the gears until the throttle is at full throttle (a slight uphill is the best place for this). After a few seconds of full throttle running, quickly pull in the clutch and stop the engine (Do not allow the engine to idle or coast to a stop). Remove the spark plug and look at its color. It should be a light tan color (for more info on reading spark plugs click here). If it's white, the air/fuel mixture is too lean and a bigger main jet will have to be installed. If it's black or dark brown, the air/fuel mixture is too rich and a smaller main jet will have to be installed. While changing jets, change them one size at a time, test run after each change, and look at the plug color after each run.

After the main jet has been set, run the bike at half throttle and check the plug color. If it's white, lower the clip on the jet needle to richen the air/fuel mixture. If it's dark brown or black, raise the clip to lean the air/fuel mixture.

The pilot circuit can be adjusted while the bike is idling and then test run. If the engine is running poorly just off of idle, the pilot jet screw can be turned in or out to change the air-fuel mixture. If the screw is in the back of the carburetor, screwing it out will lean the mixture while screwing it in will richen it. If the adjustment screw is in the front of the carburetor, it will be the opposite. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs.

Altitude, Humidy, and Air Temperature

Once the jetting is set and the bike is running good, there are many factors that will change the performane of the engine. Altitude, air temperature, and humidity are big factors that will affect how an engine will run. Air density increases as air gets colder. This means that there are more oxygen molecules in the same space when the air is cold. When the temperature drops, the engine will run leaner and more fuel will have to be added to compensate. When the air temperature gets warmer, the engine will run richer and less fuel will be needed. An engine that is jetted at 32deg Fahrenheit may run poorly when the temperature reaches 90deg Fahrenheit.

Altitude affects jetting since there are less air molecules as altitude increases. A bike that runs good at sea level will run rich at 10,000 ft due to the thinner air.

Humidity is how much moister is in the air. As humidity increases, jetting will be richer. A bike that runs fins in the mornings dry air may run rich as the day goes on and the humidity increases.

Mikuni Carburetor Tuning Manual

Correction factors are sometimes used to find the correct carburetor settings for changing temperatures and altitudes. The chart in fig 8, shows a typical correction factor chart. To use this chart, jet the carburetor and write down the pilot and main jet sizes. Determine the correct air temperature and follow the chart over to the right until the correct elevation is found. Move straight down from this point until the correct correction factor is found. Using fig 8 as an example, the air temperature is 95deg Fahrenheit and the altitude is 3200 ft. The correction factor will be 0.92. To find out the correction main and pilot jets, multiple the correction factor and each jet size. A main jet size of 350 would be multiplied by 0.92 and the new main jet size would be a 322. A pilot jet size of 40 would be multiplied by 0.92 and the pilot jet size would be 36.8.

FIG 8

Correction factors can also be used to find the correct settings for the needle jet, jet needle, and air screw. Use the chart from fig 9 and determine the correction factor. Then use the table below to determine what to do with the needle jet, jet needle, and air screw.

Needle Jet/Jet Needle/Air Screw Correction Chart

Correction factor

1.04 or above

1.04-1.00

1.00-0.96

0.96-0.92

0.92 or below

Needle jet

Two sizes larger

One size larger

Same size

One size smaller

Two sizes smaller

Jet needle setting

Lower clip position

Same

Same

Same

Raise clip one position

Air screw opening

One turn in

1/2 turn in

Same

1/2 turn out

One turn out

FIG 9

This article was written by, and has been reprinted with the permission of Doug Jenks. All rights reserved.
smallengprep@yahoo.com

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