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How can you tell if the power vavle is bad on a Holley 750 DP? Can you suck or blow on it and tell? I dont want to replace it if its good, but I don't know how to tell. The car is running bad most of the time,((After I changed the jets in the carb, but that's another story))and was told that the P/V might have gone south.. scott

I made an adapter with an old spark plug boot. The large end of the boot fits over the diaphram side of the power valve ( hold it against the metal portion ). Ran a vacuum hose from the small end of the boot to my Mityvac. You can not only see if it works, but you can verify the opening vacuum.

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