Originally Posted by
tomw
Bear: I've never seen a stuck power valve, mainly because when the engine is off the valve is in the open position
I think that a spring holds the power valve closed when the engine is off, and that vacuum in the venturis pulls it open.
tom
When vacuum drops the valve opens. High vacuum holds it closed, hence the spring holds it open. But with engine off, no vacuum means the engine does not suck and no fuel flow.