Nothing "pulls" fuel through the valve, the pump pushes it. It would starve more at higher RPM if it wasn't getting enough flow.
I used a poor choice of words. I think (just a theory) that the valve is opened just enough to allow the engine to run. But under higher vacuum loads, the diaphragm might be opening up more above 2,000 RPM where it can then supply more fuel. But under lower RPM when the vacuum is lower (I've verified this using a vacuum gauge), the diaphragm isn't opening enough to allow sufficient fuel to service the engine at lower RPM's. At higher RPM's, the vacuum pull is stronger, which might be opening the valve more (if not all the way) to allow proper fuel at highway speeds.
Again, this is just my theory.
What I do know is that the vale is not closing. Remove the vacuum line and the valve should close, and starve the engine once the carbs are out of fuel. This did not happen. This still does not necessarily mean that my floats on the left carb are not bad. Even with a failed valve, with the floats working, the fuel should not be draining into the left intake manifold. So I'm going to remove the carbs and rebuild them; I already have the kit. Plus someone put a larger main-jet in when they had the bike. I have the stock jets.
I'll pull the valve off sometime today I think. The seals might be good, but the little bushing that holds the front and rear seal might be stuck from corrosion. Or the front seal might be bad. I feel that the rear larger seal is good because it held under vacuum when I tested it yesterday.