CV and VM carbs difference?

[Fefrank]

I am thinking of buying a set of carbs a Gs1000L 1979 for my 1980 GL. someone mentioned to me that the carbs changed in 1980 from VM to CV's?. And I just want to make sure they are interchangeable, and what would be the difference between these two set of carbs, and the pros and cons to the change (if there is any).

Thanks in advance.

[tkent02]

I am thinking of buying a set of carbs a Gs1000L 1979 for my 1980 GL. someone mentioned to me that the carbs changed in 1980 from VM to CV's?. And I just want to make sure they are interchangeable, and what would be the difference between these two set of carbs, and the pros and cons to the change (if there is any).

Thanks in advance.

VM = instant throttle response, CV is a hair slower sometimes more than a hair... VMs are very simple to tune, CVs not so much. CVs are altitude compensated and run well at any elevation, VM do not compensate for elevation at all and run like crap outside of a few thousand foot window they are tuned for. For this reason I have gone to all CV bikes, they run just about perfect from sea level to 14,000 feet.

Cvs have bigger bores, and so the wide open power is slightly greater. Cvs have vacuum diaphragms which can fail and are very expensive.

The intake ports are bigger on the heads for the CV carbs, they are not really interchangeable without swapping heads.

[Steve]

I agree with just about everything tkent just mentioned, but would like to add a few more details.

VM carbs do have "instant throttle response", but that response is not always positive. If you are at low engine speed and suddenly open the throttle, the engine will bog down because there is no air flow across the jets. That is one reason the CV-type carbs were used. The "CV" stands for "Constant-Velocity", which describes the air flow across the jets. This was acheived by using the slide as a variable venturi to maintain air speed.

Racers will prefer the VM series carbs because of their quick response. They will not be bothered by the low-speed bogging because they know enough to keep their engines running at proper speeds. A CV-type carb will drop the slide during a gear change and take time to re-open it, making for difficult throttle control when using full throttle during a race. However, for street use, the BS series carbs (the CV-type) tend to be much more user-friendly because of their even response.

Yes, the diaphragms are expensive. However, I have examined and/or rebuilt a couple dozen sets of GS carbs and not seen a failed diaphragm yet. The only ones I have seen with holes were on my son's Venture, and they cost even more than ones for a GS.

.

[Big T]

lots of cons trying to replace CVs with VMs

just buy some CVs, lots of them out there

but, the question is, why are you buying more carbs?

[Fefrank]

lots of cons trying to replace CVs with VMs

just buy some CVs, lots of them out there

but, the question is, why are you buying more carbs?

I was just thinking to get an extra set of carbs just in case something inexplicable happened. Plus it was a pretty dang good price! Oh well better luck next time. Thank you all. For your info. I'm learning a lot in this forum! I can't believe how much I've been able to get into my brain in the last few weeks.