i have a 650 dp holley on my car if u rev it up slowly the runs great but if u just open it all the way up she falls on her face and then backfires though the carb a buddy told me the power valve is shot is this right

 

Could be but check the accel pumps first.

 

how do you check the accelerator pump

 

it backfires out of the front 2 barrels

 

Not to sound like a dick, but why are you running a carburetor if you have no idea how they operate? You need to seriously go out and get a carburetor book from Barns n Noble and understand how a Holley works. A carbureted car will never run right unless you tune the carb to do so. And you can destroy an engine if you're badly tuned.

As far as your problem, the accelerator pump delivers fuel as you open the throttle, it's operated by a plastic cam screwed onto the throttle linkage. Make sure it's all working properly and try a bigger cam. If the pump shot is too lean then you can get carb backfires when you hit the throttle.

 

+1 ^^^^^^^^


With the car OFF look down the barrels of the carb. Press the accelerator back and look for a small but strong stream of fuel coming from the squirters at the top of the venturies. Depending how your carb is set up the rears will follow quickly

 

Accelerator Pump Tuning video clip. LUK