my tank is not venting properly (gas cap)

Hi,
My KZ650SR-D2 runs awesome. The carbs are perfectly jetted for my 4-1 pipe and pods. I have a hard time keeping the rear wheel straight sometimes. The being said, the one problem I do have is that my tank is not venting, or rather, sucking properly. If I don't set the gas cap on exactly perfect, it starves the petcock, and I have to stop and push down on it several times to let it catch up. I have the SR tank with the key-in-the-center, pop-out cap, not the hinged one.

Any advice on cleaning this cap, it IS gummed up and corroded. Is there a good solution I could let it sit in?carb cleaner maybe? Anyone know how the vent circuit is routed in there?

On mine, you have to take the cap apart and clean it. There is a gasket and two passages that vent the tank and a small hole between the two sides. Yours is probably plugged up.