Does anyone know, off the top of their head, how the newer vacuum system of fuel shut-off works? I just got a UOA back and have a 2% fuel dilution problem. I suspect that it's the shut-off system that's failed. Fuel dilution used to occur regularly when one forgot to shut the petcock, and fuel would leak through the system and down past the rings. I'm only guessing that this is my problem, assuming of course that this is possible with the new system.
Thanks,
Frank

 

There is a vacuum controlled spring-loaded diaphram valve inside the shutoff valve. There is a vacuum hose that runs from the intake manifold to the valve. As long as there is vacuum applied to the diaphram, the valve will be pulled off of its seat. If you have a leak in the diaphram, it is possible to bleed fuel into the manifold. I replaced my shutoff valve with a Pingle valve and plugged the port on the manifold. This applies only to carbed bikes.