Holley Carb Backfiring

[Duster_340]

I have a Holley 650 #4777 double pumper mechanical secondaries.
I started it for the first time this year-it started right up but I did get a one backfire through the carb while the choke was on.
Now it runs with a constant small backfire noise throught the carb.
I'm thinking I blew the power valve-any ideas???

[ohioDemon]

i'd check the carb to manifold gasket. i've been using holleys for 30 yrs and have never had a bad power valve.

[creative1]

i have read MANY posts about holley carbs, back-fires, and powervalves. they all seem to say the same thing: if you get a backfire, chances are that you have blown the power valve, unless you have a special "back-fire protection device". i dunno what they are called... lol... someone more falmiliar with holleys should be able to help there. i run a demon, based on the holley design, i understand, but barry grant took steps to prevent this problem.

i think that a violent enough back-fire will kill the power valve in ANY carb equipped with one... and if you think they dont happen, back-fires are the reason for the scattershields on superchargers. i dunno if the powervalve would be protected or not if the supercharger explodes, though. maybe if only the burst panel pops... lol

seroiusly though, powervalves are vacuum-oriented critters. they arent intended to operate with positive pressures, especially where flames are involved.

[dwc43]

If it backfired most likely you did ruopture a power valve. I've seen many of them ruptured from a back fire. Change it first and then check your timming and other areas to make sure it does not do it again. And you can buy a kit from Summit racing to install in your carb to prevent damage from a back fire. It's a blow out protection valve.

[jelsr]

The PV is easily checked, if there is fuel in the vacuum side it is ruptured, if dry it's OK.