I have a new Holley truck avenger. It has the new anti blow back power valve in the carb. I had a bad back fire the other day and now i have a miss, what are the symptoms of a bad power valve.....There are no vacumm leaks that i can find and it just had tune up less than 3000 miles ago..Any idea's anyone.

 

A blown power valve will cause an extremely rich condition. You'll have a rough idle and possibly black smoke in the exhuast. I'd start diagnosing the miss with a compression test.

 

A quick way to check for a blown power valve is to turn one of the idle mixture screws in. If the engine stumbles and tries to die, it's probably ok. If the engine doesn't change, it's probably blown. I've blown a few power valves with the "protection kit" installed.

Actually, this is a good test for any internal fuel leak. I have also seen cut O-rings on the accelerator pump transfer tube, and gaskets that don't seal the metering block to the main body also cause internal leaks.