You're close but off the mark. What that valve does is allow extra air into the intake on high vacuum situations, i.e. deceleration to keep deceleration from being too harsh. If it wasn't closing it just wouldn't idle and if it didn't open you would probably learn to refrain from closing the throttle too quickly.
Thanks for the correct. In fact, that was my problem before replacing the valve which had a slow vacuum leak from a crack on the bottom side of the valve. I was going to simply epoxy the crack until I noticed it failed the vacuum pressure test according to the maintenance manual. Using a small vacuum pump, the first test requires vacuum pull be applied to the lower port and the vacuum should hold; it did not hold and leaked down after about 2 to 3 seconds. The second test is to apply vacuum to the upper (smaller) port and apply 5psi pressure to the lower port; when vacuum is released, the valve should open and the 5psi air blows out the opposite side large port on the other side of the valve. The cracked valve functioned but was too intermittent. So I was lucky enough to find a fully functional one on ebay for $24 bucks (new one unavailable/discontinued at $160 bucks), and I tested it before installing the used one; it checked perfect. So now the bike idles much better, whereas before it would fluctuate dramatically between 800RPM to 1000RPM. So replacing the valve solved that problem and also improved acceleration.
Unfortunately, I am still having the jerky problem under 2,000 RPM at 1/2 to full throttle all gears.
Also, before I replaced the valve, you are quite right; I learned that snapping the clutch on high-vacuum RPM causes the rear tire to lock up while in a turn...this happened to me and was quite scary. LOL Since replacing the valve, this does not happen anymore, and in fact my deceleration is very smooth. I do not know what to do if this valve goes bad because I had a hell of a time finding this one. And Honda cannot get a new one because they do not manufacture these valves anymore.
Thanks for the inputs bro. I'm actually learning quite a bit about this bike. Despite what most would believe, I think Honda makes some of the best cruisers on the road; especially the Goldwing which in my opinion is superior to the Harley's. Don't tell that to Harley fans though. LOL I've blown 4 Harley Davidson's off the road so far with my Goldwing; actually beat an Ultra Glide, a Road King, and even a Screaming Eagle.
Long live the Goldwing!