How do you know when a power valve is blown?

I've got a 650DP and it backfored today and nearly took my hearing out.

Vince

Hey Vince,your car would run real rich at idle,close to fouling your plugs rich.If your Holley is a newer version it should be equipt with a power valve saver...just a check ball in the return orifice.Was it a misfire or lean exhaust back fire? C-yaa, Vince O1

If car runs like crap your exhaust is black the plugs to.And look down into carb. if its leaking buy, take it out and suck on it :D

Sounds like you need to check your timing.Float level,air mixture.