Archive for the ‘VM’ Tag

XS650: Yamaha Racing Tips   Leave a comment

This manual first appeared in 1972. Here is the 1973 revised edition. Includes Section 11. XS750(650) Racing Special.

The OW72 motor was developed to take this and the then relevant associated tuning knowledge to another level.

Racing Part numbers referenced in this are found in the Yamaha Racing Parts Book.


Yamaha Racing Tips … mostly for the 2 stroke program … includes Section 11 XS750(650) Racing Special


YRT contents


YRT contents


YRT warning


Here are the sections. Relevant to XS650s are Sections 1 and 11 …

  1. Using a degree wheel,
  2. Tips for cutting parts,
  3. Cylinder Head mods,
  4. Porting mods,
  5. Piston mods,
  6. Rotary Valve mods,
  7. Con Rod mods,
  8. Expansion Chambers,
  9. Spark Plug selection,
  10. Carb Adjustments

Posted July 22, 2013 by xscafe in Manaul - Literature, Manual - Other

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XS650: More VM   Leave a comment

Mikuni VM Carbs


Sudco – VM … vm info… parts etc


also see

Carbs … Mikuni

VM34SC Mikuni

Posted May 6, 2012 by xscafe in Carb - VM

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XS650: VM34SC Mikuni   Leave a comment

Yamaha’s Racing Tips Manual, 1974, suggested using VM34SC Mikunis. Round slide. Magnesium bodied. No Power Jet/Accelerator Pump/Beschleunigungspumpe.

Today, TM’s are supposed to provide significant performance improvements. Flat slides and the jet blocks help create a smooth bore effect. Air flows faster and smoother through the TM Series venturi. Higher air flow velocity gives a stronger vacuum at the needle jet needle. Provides more precise metering and better throttle response.

For known geographic and climatic conditions.

However, I do a fair bit of touring. Low to High altitude. For this I actually prefer the original BS series carbs. They automatically adjust themselves for air pressure. Easier to keep tuned.

… VM34SC carb … XS750(650) Racing … adjustments … jet needle 6F9 (#2 clip position)


… carb adjustments


… carb .. VM34SC … adjustment


… VM34SC carb … 3/4-full throttle adj … main jet



… VM34SC carb … 1/4-3/4 throttle adj … needle jet


… VM34SC carb … 1/8 – 1/2 throttle adj … slide adj and cutaway



… VM34SC carb … 0-1/8 throttle adj … air mixture screw – pilot jet



… VM34SC carb … idle speed screw

Posted December 21, 2011 by xscafe in Carb - VM

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XS650: Carbs … Mikuni   Leave a comment

I’m not a carb expert. I can strip, clean and tune my own carbs fine but if I was relying on my powers of fine tuning for a living I’d be in trouble. It’s just as well the original CV carbs are fairly straight forward.

Many of their problems are related to dirty tanks leading to blocked Pilot circuits, float valve, float level setting, airleaks in vacuum barbs, boots, butterfly shaft or air filter.

Good discussions of these have come out of the Garage.

Mikuni_BS-CV_Carburetor_Rebuild_Tutorial … a nice pictorial guide

BS34 and BS38

VM 34-36 Roundslide Mikuni

Here is a Mikuni VM manual

vm carbtune

Interesting read on CV carb setting up

Basic carb theory


jet crossover


Repair hints


VM Jetting chart

Topham resource site

2 types of original carbs, both CV, see the Oz site too

  • BS38 – early types were not linked and bolted perpendicular to the head, later models were linked and the boots were angled to the head
  • BS34 – linked and angled to the head


Basic CV carb ID pics


US XS650 carb guide


pilot jets


float setting


CV cut-away


CV schematic … BS34 pilot jets are fed directly from the main so must be plugged


VM dimensions


Goran Perssons vacuum port mod


This is handy for providing vacuum points to balance your carbs if using boots without vacuum barbs, simply plug when not being used.

Posted January 10, 2011 by xscafe in Carb - Boots, Carb - BS, Carb - VM

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