I lightened down my bike considerably. All the electrics went. Run batteryless. Removed the air-boxes. Left the whole section under the seat empty.

Looks cool. No good for the motor.

Had a pair of el-cheapo pods lying around. More or less the right diameter, according to the label. After fitting I decided I could do better:

 

now how are you supposed to get a good seal there? … also see the cracking along the edges – this was new out of the bag!!

 

big inner lip … everything restricted … diaphragm vacuum port at the top: pilot air jet-lower left: main and mid range air jet-lower right: bowl vents in the middle

 

these filters had never been used

 

was then given, under protest, a set of these

 

larger surface area

 

no restricting step

 

very thin walled … rubber may not hold up esp. with no support … wonder how long it will last … is the rubber ethanol proof?

 

• very thin
• where-ever you look the filter wants to break out of the rubber
• see the large hole in the flange lip? WTF?
• strong enough to hang unsupported?
• ethanol proof?

Not an optimal solution. But heaps better. Will have a look around for a K n N to compare.

When I think about it I guess I should add here that pods generally increase engine breathing capacity. The immediate effect is to lean the carb mix. More air, less gas. Pistons and valves don’t like this. Get a little intimate with your carbs. Odds are you may have to massage your jetting.

Reading will tell you. Chop those plugs.

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

Sudco

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.