Ok I have a Holley 750 vac. sec. carb. It stumbles bigtime off idle and I have checked and fixed everything and the stumble does not go away. So ive been told its a blown power valve. My question is what exactly is a power valve, where is it located on my Holley and where can I get a new one. Thanks

The power valve is located on the primary side in the metering block, the metering is the peice between the fuel bowl and the main carb body. it will like a 1" hex nut with a spring loaded rubber poece inside. Are you sure your timing is set correctly?

Yes ive gone over it a million times. I guess ill tear it apart this weekend

I had the same thing. I tried replacing the power valve with the same and various sizes but it never helped. I ended up with a different pump shot cam and next size larger primary jets with different initial timing. None of this applies to you however if it ran great before and this problem just started.

I have had the same SEVERE stumble off idle on my 454 and I can tell you for a fact that it was not the power valve. I replaced it with three different ones and none of them made one bit of difference. I would have to agree with going to a bigger pump cam and also if you haven't tried it already, put a 50cc accelerator pump on it.

Had same problem in past, messed with accelerator pumps and squirters alot but still couldnt get it right. Went up a couple of jet sizes on primary side and solved problem. Also if the throttle shaft bushings are worn it will draw air in around shaft creating a lean condition wich will also cause an off idle stumble.

Thanks

Originally posted by CheZeppelinCorps:
My question is what exactly is a power valve, where is it located on my Holley and where can I get a new one. Thanks Remove the bowl, then pull off the emtering block (usually stuck to the carb body) and on the back is the pv. Replacements can be bought at Advance auto, Summit, Jegs, speed shops, etc.