Power Valve Bad?

No, but it will mean that you'll have to lower the float. If the float level is too high, you'll get fuel dribbling out the boosters causing a major rich condition. Let me add that the car must be running when you check the float level.

If this doesn't solve your problem we'll have to look deeper into the problem. Do you know how vacuum your engine is pulling at idle, in gear?
This is what I was thinking too. Also, if the back float is high fuel can slop out of the bowl vent when you hit the brakes, stalling the engine.That was what grabbed my attention.