Archive for the ‘BS38’ Tag

XS650: Carb Heaven   Leave a comment

1:1 – In the beginning was created the heaven and the earth.
1:2 – And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit moved upon the face of the waters.
1:3 – Calling, ‘Let there be light’: and there was light.
And not before time too! Sonar never really worked for me. No fun riding the XS by white cane.
Ever wondered where carbs go when they die.
Carb Heaven? Sonic bubble bath. Soda spa. Queen Joan Jetts.
Or Carb Hell? Oxidation soup. Vacuum Patches.  Dysync city.
Function change? Why not …
  • dual eyes … halogen


1 .. halogen eyes

halogen eyes



2 .. simple really

simple really



3 .. coloured and polished variations

coloured and polished variations


Where are you  going to hide all the spaghetti?

Mount as you wish.

  • stop/tail … led



4 .. ol led eye

ol led eye



5 .. here's lookin at you ... led

here’s lookin at you … led



Not really my cupoftea, but (?) … rcknrllrog on fleabay

Posted October 13, 2011 by xscafe in Elec - Lights

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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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XS650: Carb Boots and Diaphragms   1 comment

Some time ago I had to rebuild my carbs, BS34s from a 3L1 motor, was really no big deal, they had been sitting a while so I cleaned them and tarted em up. Rejetted, new needles. boots, diaphragms etc.

The original Yamaha boots were hard and cracking after just 30 odd years. Anyway I ordered new boots etc and installed the carbs. After 3 months the boots had cracked to shit on the outside and begun to melt on the inside. WTF? And European fuels dont have the same ethanol content as North American-I see the other day that this will be changing in the near future. This was my first experience with that particular supplier I cant even bring myself to name, but we all know who he is with his cheap chinese crap.


1 .. damage like this

damage like this


2 .. and this

and this


Anyway, to cut a short story longer, JBM Industries came to the rescue. Theyve been making stuff for the aircraft industry.

These boots dont use the original metal cage and will secure your carbs unsupported. They make BS38 boots both straight and angled flange and BS34 boots. Also the diaphragms.


3 .. NOTE. These will have no problems with ethanol containing fuels.

NOTE. These will have no problems with ethanol containing fuels.

My BS38s are running great. It’s a shame as I prefer the BS34s. I guess it’s good that Paypal is my friend.

JBM’s first carb diaphragms were for our Mikuni CV BS 38mm. Next were those for the BS 34’s. They’ve gone on to design and manufacture parts and compression molding tooling for a variety of vintage motorcycle carburetors. Don James, head of JBM, uses only a specified quality TSR heat cured compression molded rubber compound. (Not that crap recycled, zero quality control crap we are becoming used to from my favourite low service partner). Molds, tooling and production are all done ‘in house’.

TSR … Technically Specified Rubber, a system for describing rubber compound formulations. Graded according to dirt, ash, nitrogen, volatile matter content and the Plasticity Retention Index (PRI).

A first rate design, tooling and molding operation with excellent customer service!

Cost is very reasonable. Reflects a lack of ‘middlemen, mark-up merchants’  (distribution/wholesale/retail links). Products sold directly at a reasonable margin to the customer/user. A sound business model.

JBM Industries – thumbs-up – keep up the good work guys.

Posted January 10, 2011 by xscafe in Carb - Boots

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