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

Tagged with , , , ,

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: