I am blowing out the power valve on my T/A. I had a 6.5 in it now putting a 7.5 in it as that was what was in it the first time. Any suggestions on which one I should use? What might be blowing them out? and if anyone has installed the blow out protectors? Thanks, Kirby

I don't know how things are these days but back when I had my hands into a Holley several days of the week, here's what fails them in no particular order.

FIRST I've found many leaky right out of the box. This (back then) used to include several brands and carb kits as well as Holley originals

SECOND Backfireing (cold start, retarded timing, etc) back through the carb

THIRD Wrong/ bad gasket

FOURTH Overtorquing the valve can damage it

The valve you need has nothing to do with blowing it out. It has to do with when the valve opens compared to intake vacuum.

Also, how do you know for sure that "you are blowing it out?"

The one I took out had gas behind it. I am assuming that the one I replaced has blown as well, as it suddenly started to run crappy, and identical to how it ran before I replaced the first one. I was asking which P/V SHOULD be in there, if there was a specific one that should be used (for tuning) not as a cause of the blow out.

Most of the new versions are supposed to be 'Blowout Proof', whatever that means. Usually the only thing that will break the diapraghm is a backfire thru the carb. Most guys use a PV # that is 2 to 4 numbers below their vacuum reading at idle (in gear for an auto, I think). On my mild build 440-6 motor after some experimenting I found that the 'traditional' 6.5 PV wasn't getting the job done. My motor (stick) idles at 16-17" of vacuum with a mild street VooDoo cam. I put in a 8.5 PV and it made a huge difference in the transition from idle to part/full throttle.

The blowout protection is just a one-way ball check-valve that you install in the vacuum port at the base of the carb. Holley has been including them on carbs now for about 6-8 years. But the installation of the check valve in an older carb without is extremely simple. As I recall they even include the drill bit.

Usually only a backfire wrecks the powervalve.Have you checked the float level? Once in while the car will run well when it's cold and when it is hot and idling the bowl level gets too high and makes the engine load up and it seems like a bad power valve.Check the vacumn in gear if it's an auto and get the correct valve.

1/2 of your manifold vacuum reading at idle in gear for auto or in neutral for stick for a PV size is a good start.