Thread: power valve

Tweet

What does a power valve on a carburetor do? Does it increase your engine vacuum if it's to low? If you carb doesn't come with one, where does it go?

A power valve richens the mixture when the engine is under a heavy load. The Holley style power valves use a vacuum signal to make it work. The vacuum affects the valve. The valve has no affect on the vacuum.


When you nail it (make power) the vacuum drops. When the vacuum level falls below the spring pessure the valve opens a port letting more fuel into the air stream making more power. When you let up on the gas the vacuum builds back up overcoming the spring pressue closing the port. You can buy power valves with different rated springs to open at different levels of vacuum for different applications. (wild cams or multiple carbs)

Holleys used to be famous for rupturing the power valve diaphram if the engine back fired. With a broken diaphram, the spring opens the valve even when it's not needed adding too much fuel for the load on the engine. The engine runs too rich at idle. I think their new carbs have corrected this common problem and I think I read that they have a retro-fit kit for the old Holleys.

The Holley techs said never pump the gas while starting the engine. Turn the key off, pump the gas, let up on the pedal and then turn the engine over.

yes this is and way to go if you have the old holley just make sure you set the drill stop right or the ball and a assembly will fall out the bottom of the base plate and the power valve is for richment like 32 tom said very good job 32 tom

Thanks for the info Guys, wasn't quite sure of where it went.