Swap Bs32 with VM26?

[koolaid_kid]

This has got me wondering... I realized that the good set of rebuild rejetted VM22SS carbs we have on my wife's GS550 will be too much work and slightly different spacing to fit onto the BS32 equipped GS650G head we're swapping on. I was wondering if the GS750 VM26's would be adaptable to the BS32 intake boots. The ports on the 650 head are MUCH MUCH LARGER than the older GS550 engine.

The GS750/VM26 "bogging" issue you mentioned has me wondering if it was just a tuning issue. The BS carbs I was told are more prone to a slight lag when cranking the throttle, because the needles are operated based on engine vacuum on the diaphragm, and when you gun it really quickly, the engine vacuum drops a lot momentarily, resulting in the needles dropping (leaning out) momentarily before they raise up. The vacuum operated slide needle seems better for streetability, smoothness, and economy, but with a manual/mechanical slide carb, it is garaunteed that you are not going to momentarily lessen the amount of fuel restriction through the mains when you crank the throttle rapidly.

The bike was right off the showroom floor. I don't pretend to be an expert on the VMs, but Steve explained it was the immediate drop in vacuum that is the issue, which is why the CVs do not do that, the slides raise slower, allowing the slides to rise gradually.

[Steve]

The bike was right off the showroom floor. I don't pretend to be an expert on the VMs, but Steve explained it was the immediate drop in vacuum that is the issue, which is why the CVs do not do that, the slides raise slower, allowing the slides to rise gradually.

ALL carburetors depend on having air moving across the jets at sufficient velocity to lower the pressure in the venturi to draw fuel up through the jets.

If you are running at a relatively low throttle opening (VM or BS carbs), your velocity will be high. If you suddenly whack the throttle open on the VM carbs, the engine, which has been creating a vacuum against the closed throttles, will suddenly have that vaccum filled with a rush through the carbs. Once that vacuum is gone, there is no longer sufficient air velocity through the venturis to draw the gas up through the jets.

If you try the same trick with the BS carbs, the slides will likely be in a lowered position because there is not much air moving below them (their position has NOTHING to do with engine vacuum). When you suddenly open the throttle butterflies, the lowered slides will ensure that the air velocity remains high (that's why these are "CV" carbs, that stands for "Constant Velocity"), allowing the jets to still do their job.

When there is not enough air velocity, there will be no fuel to burn. That can be alleviated by adding an accelerator pump, but I know of only ONE GS bike that has one.

.

[koolaid_kid]

Thanks, Steve. Irritated the crud out of me, since I was young at the time and pointing the wheel at the sky was a big thing. These days, not so much.
There were other brands (Kaws?) that had a few models with the accelerator pumps, but CVs fixed all the issues.
My XS650E had CVs, which confused the heck out of me. I pulled the top off one of them, expected to see a slide just like all my 2 strokes and early Hondas had. Instead, there was this rubber diaphragm thing. ??? I immediately put the top back on and left it alone.

[Bookmon]

first glance- I tought it was swapping the B52s. I was in for that deal. I will swap them for Justin Beiber any day. Poor kids of today- their music choices are rather poor.