MIKUNI VM CARBURETOR - Vintage Snow

1 MIKUNI VM CARBURETOR . SUPER TUNING .UAl nil: MIKUNI ~!:'M~K~!~~~N~2~~E~RATION. CALIFORNIA 91324 EXPLODED VIEW. 1. Rubber Cap, Throttle Cable :===i 2. Cable Adjuster 30 29 3. Locknut,. Cable Adjuster 4. Top, Chamb er 5. Tube, Air Vent 31 6. Spring, Piston Valve 7. Plate, Needle Retainer ~. 3 8. "E" Ring 18 9. Jet Needle 4 15 10. Piston Valve 11. Needle Jet 12. Rubber Cap, Starting System 16 13. Cap, Starter Plunger 14. Lever Assy, Starting System 6 15. Leaf Spring, Lever Positioning 28 17 16. Spring, Starter Plunger 19 17. Plunger, Starting System 18. Body, Mixing Chamber 19. Gasket, Float Chamber 21 20. Baffle Plate, Flost Chamber 2 21- Pilot Jet 7 3. 8 5 22. Pin, Float Arm Hinge 23.

2 Float Arm 9 20 24. Float 25. Float Chamber 35 26. Washer, Float Chamber Plug 27. Plug, Float Chamber 28. Air Jet 36 29. Air Screw 34 30. Spring, Air Adjusting Screw 31. Spring, Idle Adjusting Screw 32. Screw, Idle Adjusting 33. Washer, Needle & Seat Assy 2 34. Needle & Seat Assy 35. Cup, Fuel Retaining 36. Main Jet 11 37. Plate, Vent Tube Retaining 2 38. Screw, Float Chamber 2. 37. 2. 27. I 38. PARTS LIST. 008-49 VH30-44 VIl3Z-33 VIl34-Z0 Vll36-4 Vll38-3 YlII<0-4 _4-3 008-49 VI00-44 Vll32-33 Vll34-Z0 Vll36-4 008-3 Yll40-4 "44-J. 1. 006/46 M6/46 1IM26/46 VH26/46 VH26/46 VM26/46 VH26/46 VH26/46 2D. MSI227 VM341114 VlO41114 Yll34/114 Yll36/40 VI06140 004120 VH44/Z0. 2. M21/14 HZ!

3 /l4 M21/14 M21/14 M21/14 K21/14 1<21/14 M21/14 21. VM22/210 VK22/210 VK22/210 !210 VK22/210 VK22/210 VM22/210 VM22/210. 3. !J0/247 830/247 B30!241 830/247 B30/247 .30/247 B30!241 22. BV26/22 BV26/22 BV26/22 BV26/22 BV26/22 BV26/22 BV26/22 BV26/2:2. 4. VK26/56 VM34/27 VH34/21 YH34/27 VK36/45 VMJ6/4' VM44!OS VM44!05 23. VH28/166 VM34173 VM34173 VM34173 VH36!15 VM36/1S VK36/15 VM36/15. 5. VMl7/173 1IM28/78 VM28/78 VH28178 VH28/78 VM28178 VM28178 VH28178 24. VM28/164 VlO4/61 VM34/61 Yll34161 004/236 ""241236 ""241236 VH24/Z36. 6. 1IM24/195 Vll34/50 VH34/50 004155 004155 004155 _4/13 VM44111 25. VH281130 VlO4168 VK34168 Yll34168 006/33 VH36133 004104 VIl44/D4. 7. 008/132 004/31 VH34131 004131 VMS5109 005109 _4/09 OO41D9 26.

4 1IM281134 1 III281Z54 1IM281254 0081254 008/254 1IM28/2S4 0081134 1IM28/U4.. 8. 10. IIM2D/369. J8-5P21. VK28/S6. 0001369. J8-6]'5. \lM34!110. 1IM20/369. J8-6DP5. V!04/110. 1IM201369. J'S-6 Oft3. YM34/110. 1 III2DI369. J8-6!'J6. VM36/36. 0001369. J8-6 DPl 008/24. 8&32/126. JS-iF6. VM40/02. BS32/126. J8-11'6. VM40/0Z. 27. 28. 29. 1IM281133. BS30/97. VK20/214. 0081253. 8530/97. VK20/214. 111128/253. B530/97. VM20/214. VM2S1253. B530/97. VM20/214. VH28/Z53. BS30/97. VK20/214. VM28/253. B630/97. VM20/214. 0081133. B530/97. VM20/214. VIl2S/UJ. 8530/91. VH20/Zl4. 11. VK30/38 VK34!OS. VH34/05 YM34/0S VM34/0S VM34/17 VH44/10 VM44/1D 30. Kl2F/46 MlIl/46 MI2l/46 Ml2l/4b Ml2l/46 Ml2F/46 M12F/46.

5 12. VK20/4S5 VM20}455 VM20/455 H20/4SS VH20/4SS VK2D/liS5 VM20/455 31. H20111 .20/11 1<20111 .20111 .20111 .20111 .20/11 1<20111. 13. MD16/3D IIM2D/456 IIM2DI4S6 "Z01456 1IM201456 VIl2DI456 IIM2DI456 VH2014S6 32. VM241224 VH281142 004/390 0041224 002/171 VM22/171 0041224 002/171. 14. VH28/497 1IM28/1Z4 1IM281124 VH281124 VMS6158 006158 VH36/58 1'>126158 33. VM26125 Bl4/52 834152 834152 83415Z 834/52 834/52 834152. 15. 006/0. VI02/17 VI02/17 VI02117 1IM26109 VH26/09 "26/09 1IM26109 34. VM26/26 VM34/39 VK34/39 VM34/39 VK34/39 VH34/39 VH3413'9 VM34/39. 16. VKl6/42 VMl6/42 YMHi/42 VMl6/42 VKl6/42 VMl6/42 VMl6/42 35. VM28/228 VM36/17 \I!06/11 VK36/17 VM36117 VM38/09 VK2B/228 VH2B/22.

6 17. VK26/116 VHl8/144 VMl8/144 YMl8/144 \'Kl8/144 VHl8f144 VMI8/144 36. 4/042 4/042 4/042 "/042 4/042 "/042 4/042 4/042. 18. VK28S5 YMJOSS \lM32SS YM345S VH36SS VM38SS VM40SS VH44SS 37. VKlS/164 VH28/79 VK28/19 VK2B/79 VK28/79 VH28/79 VK2B/79 1IM28/79. 19. 0081129 004/86 004186 1IM34186 VMS6/ZD OO6/Z0 006/20 006120 38. CWZ-0416 C112-0516 CIIZ-0516 CIIZ-0516 <>12-0516 OW2-D516 CWZ-D516 CIIZ-0516. Foreword This manual is intended as a guide for users of MIKUNI carburetors who want to learn the adjusting method to the best performance from our products. In motorcycles, special tuning of the engine is now considered a routine practice. The arrows that appear in the drawings in this text show the direction in which air, fuel and an air-fuel mixture flows, respectively.

7 JAir Fuel "Mixture Mounting angle fore and aft inclination of the carb should not exceed approx 20 degrees from horizontal. r- -- - --- -- -- -- - --- - ---~- ----- --- -- - - -- - - - - -----""]. r -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -, I. I I. I I. I I. : ~! I UI. I I. I I. I I Jet needle I : I I. I I. : I. : Throttle valve : I I. ~! Air jet Float Needle balve~. Pilot jet I. I. I. I -, I. I I I '''--Ring ~~~~:~~===~~:~~:=~~~-~~===~============= ~-=======~. c:::::;> Ai r ~Fuel "'Mixture TABLE OF CONTENTS. 1. What is a CARBURETOR ? .. 1. 2. Air-fuel mixture ratio .. 1. 3. Function and construction .. 1. 3-1. Low-speed fuel system (pilot system).

8 2-3. 3-2. Main fuel system (main system) .. 3. 3-2-1. Primary type .. 4. 3-2-2. Bleed type ..4. 3-3. Float system ..5. 3-4. Starting device (starter system) 5 ~6. 4; Tuning up of engine and selection of aperture of CARBURETOR .. 6. 4-1. Selection of aperture of CARBURETOR .. :.. 6 - 7. 4-2. Sizes of MIKUNI carburetors 7. 5. CARBURETOR setting 7. 5-1. Selection of main jet ..8. 5-2. Selection of needle jet and jet needle .. 9 ~ 10. 5-3. Pilot jet and the slow system ..10 -11. 5-4. The cutaway size of throttle valve .. 11. 6. Maintenance .. 1 2. 7. Tuning up of CARBURETOR for racing .. 13. 7-1. The amount of incoming air in relation to meteorological conditions .. 13. 1. Function of a CARBURETOR The function of a CARBURETOR is to produce combustible air-fuel mixture, by breaking fuel into tiny particles (in the form of vapor) and by mixing the fuel with air in a proper ratio, and to deliver the mixture to the engine.

9 A proper ratio (mixture ratio or air-fuel ratio) means an ideal air-fuel mixture that can burn without leaving an excess of fuel or air, Whether the proper mixture ratio is maintained or not holds the key to the efficient engine operation, 2. Air-fuel mixture required by the engine (Fig. 1). The ratio of a mixture of fuel and air is called the mixture ratio or the air-fuel ratio and is generally expressed by the weight proportion. Theoretically, the amount of air required for complete combustion of 1 gram of fuel under normal conditions is: MI'xt ure ratio = 15 gramsofoffuel 1 gram air . t ure rati10. ".. th eoret'rcaI mix In reality, varying mixture ratios are required for the engine, depending on operating conditions.

10 Although the required mixture ratio varies more or less with the type, the cooling efficiency, etc. of the engine, the mixture ratio shown in Fig. 1 is required for ordinary engines. In the high speed Air-fuel mixture Maximum power mixture ratio range, the ratio of about 12 to 13 grams of air for 10:1. 1 gram of fuel produces the maximum output. 12:1 . 14:1. However, in the case of an engine with low 16:1. cooling efficiency, a somewhat richer mixture (10. 18:1 Theoretical mixture ratio to 12 grams of air against 1 gram of fuel) may be required to prevent seizure of the engine. 20 40 60 80 100. Throttle valve opening (%). Fig. 1. 3. Functions and construction The engine of a vehicle is operated under a wide range of conditions, from idling with the throttle valve (1) remaining almost closed to the full load (the maximum output) with the throttle valve fully opened.