CV or VM what's the difference?

[wishy]

Ok dumb question, but coming from a dirt bike only background I haven't been around these street bike cv things. What I think are cv carbs anyway.

So, my '81 GS650 has CV carbs correct? They have what I call a mixture screw on top front of carbs. No other external adjustments? I guess a few pictures of the difference between the vm or cv would clear things up?
VM still a vacuum style of slide? I guess I understand the principle behind how they operate, at least what I call cv carbs, I just don't know visually what the difference is between them.

 

[chuck hahn]

VMs are mechanically linked to the throttle rod where as CVs arent. Vms WILL NOT have a butterfly on the engine side and CVs will. CVs work based on airflow from the cylinders intke vacuum. VMs work by lifting the slide mechanically and thus allowing fuel into the cylinders....basically

 

[chuck hahn]

Other than the mixture screws at the top of CVs there re no other external adjustments other than the carb sync screws..but they dont effect fuel to air ratios and such.

 

[hampshirehog]

You'll have a slow run knob on those carbs as well. Stating the obvious but just in case.

 

[JTGS850GL]

CV's will give you many benefits over VM's. Crisper throttle response and automatic altitude correction to start with.

CV Carbs:

VM Carbs:

 

[Steve]

Also please keep in mind that "CV" is a TYPE of carb, not a model name. It stands for "Constant Velocity", which is achieved by the slide moving up and down in the venturi. It should really be called a "Variable Venturi" carb, which is a bit more accurate. Because the size of the venturi changes, the velocity of the air going over the jets is somewhat constant, hence the "CV" moniker.

CV carbs are made by many manufacturers. The ones that are used on our GS-series Suzukis are all Mikunis, most of them are BS32SS or BS34SS. The '83 and up 550s had a version with siamesed barrels that were BSW30SS.

.

 

[jsandidge]

What does "VM" stand for?

 

[hampshirehog]

What does "VM" stand for?

It doesn't stand for anything. It's just the series designation.

 

[Steve]

What does "VM" stand for?

Not much of anything, as far as we know.

Pretty much like the "BS" in the CV-type carbs. What does that stand for?

.

 

[wishy]

Okay that clears it up. Never heard the VM terminology before so all the rambling carb this and that posts got me wondering what the difference was. I knew that CV was a type of carb not necessarily a exact model. I have made many old bikes run over the years never heard the VM term though.

Thanks for the info.

 

[Steve]

"VM" is the model name for the carbs on the four-cylinder GSes before 1980.

Depending on the size of the engine, they were VM22 or VM26 carbs.

It's sorta like the "GS" in the model name of the bike, it's just some letters to tell you what it is.

.

 

[hampshirehog]

VM is the designation given to a complete range of carbs of similar design fitted to many, many different bikes produced by many different manufacturers. It's possibly the most widely used carb in the last 40 or so years.