Hey Sport, here's a simple check you can use to verify whether or not the power valve is actually blown:
Turn the idle mixture screws all the way IN. If the engine dies, the power valve is good.
One other thing, every Holley carb mfg after 1992 has the check-ball modification done to them and that has virtually eliminated blowing power valves as a result of a back-fire.
Also, once you know how much vacuum your engine is making (warmed up and at idle - neutral with a stick or in-gear idling with an automatic), you can divide your vacuum value by 2 (1/2 the vac reading) to verify your power valve matches your cam. If you're running a long duration cam you may need to change the PV to match your true idle vacuum value. Any reading above 13 in hg should work with the standard PV. If you land on an even number, drop DOWN to the next size PV to get you where you need to be.
I hope this helps.
Southernman
