vm vs cv

[smokie]

Ive heard from numerous people that the j and k model gt's with the vm style carbs performed slightly better than the later style cv's, any fact to this? I guess the cv's stay in synch better? I havent touched mine in 2 years and throttle response is still as when I first set them. Mine has vm's.

[Suzsmokeyallan]

Its a known fact that two stroke engines do not have the high intake vacuum like four stroke engines. So putting CV carbs that work better on a high intake vacuum engine onto a two stroke makes the throttle response somewhat delayed and sluggish.
So why did they put the CVs on the Buffalo??? its mind boggling for sure and defies all logical thinking performancewise, but they did name those carbs the BS model...LOL

[Buffalo-guy]

Ive heard from numerous people that the j and k model gt's with the vm style carbs performed slightly better than the later style cv's, any fact to this? I guess the cv's stay in synch better? I havent touched mine in 2 years and throttle response is still as when I first set them. Mine has vm's.

Smokie.
I guess it all depends on what you mean by performing better. My J model consistantly gets about 55 to 60 miles per imperial gallon, thats about 45 on yours. Along with the generous mid range torque for passing power, I would call that good performance. If you base it on power only, then the later GT's with the more agressive porting is the way to go. But to quote Allan, the "BS" model CV carbs are definitely that, all bs. They definitely measure 40 mm at the throttle plate, but when you look down the venturie, they definitely are not. My performance enhanced buffalo makes much better HP on stock 32mm VM's than any I've seen with CV's. Just think of the ferocious power that a stock H2 Kaw makes with only 30mm VM's. They just plain breath better, and run more efficiently. I suspect there will be rebuttle to this, but this has been my experience so far. Cheers.
Fred, The great and almighty Grand Poobah of the Loyal Order of Water Buffalos, Calgary chapter. LOL.

[rngdng]

I agree that the VMs are the way to go. I have 34s on mine, and it kicks ass. The VMs (BS40s), hesitate when you punch the throttle.



Lane

[Suzsmokeyallan]

I only keep those BS things on there since the 76 is a stock bike and so i want to maintain that look.
If it was not for that fact id have tossed them eons ago and put on some 72-73 Buffalo carbs i have for it.
Considering how the BS ones work id say they actually are down on throttle response and up on fuel consumtion just as you stated Fred.

[tz375]

Fred touched on the heart of the matter when he said "define performance".

Let's start with size - we know that matters. CV carbs are not measured the same way as Slide carbs mainly because the venturi is anything but round. In the case of the GT750 carbs, the BS40 supposedly gives the same power output as a VM32 and flows similar amounts of air as a VM.

The closest comparison on stock bikes is to put a 73K head to head with a 74L. they have the same porting and pipes but different carbs. You should find that the power is the more or less the same at the same revs, so from that perspective it's the same performance.

What Suzuki did was to change from a carb with a quick response to one that has a smoother response. That makes the bike feel smoother on the road, but it feels less powerful because it lacks the "bite" or responsiveness.

CV carbs are very reliable and are good carbs but they are sluggish to respond and for many riders today that makes them feel slower

The other issue with BS40 is the changes of section internally from around intake to large to an almost square section at the venturi to a 40mm round outlet. And that is not one smooth change but several abrupt changes with sharp angles to make things worse. Then, there's a butterfly in the outlet to obstruct flow and a vacuum tube in the center which can't help either.

It is possible to port a BS40 to considerably increase air flow but it takes time and some very small rotary cutters. But that doesn't improve the responsiveness.

To increase the rate of change, one would need to allow a faster change in pressure to both sides of the diaphragm and that's hardly worth the bother.

To keep this all in perspective, most 4 strokes used CV carbs for the same reasons and they open at a similar rate to the BS40. Watch the slides on an FZR400 or Gt750 and you will see that neither snaps up, but that doesn't seem to hold the FZR back because it's not just about the slide.

In the real world either keep the BS40s for a smooth ride, or slip on a set of 34mm carbs which make more power across the board and have the added advantage of reacting faster to throttle inputs so they feel sharper.

Or add flat slides and a decent porting job and a set of chambers and let the inner beast out.

[markj]

Accellerator pumps would probably help out a lot in this area.

[rngdng]

I rode Ed Zunz's 72 GT750 which happens to have a 75 engine with the original 72 carbs. With stock exhaust and airbox, it does really cool power wheelies (in first gear), something my stock L model (now Kevin Lilly's) wouldn't think of doing. Good combo.



Lane