I know this is probably a simple question but I'm gonna check/change my power valve and need to know where to find it. Any pictures or illustrations showing exactly where the pv is?....Thanks

The power valve screws into to metering block which is the plate that is sandwiched between the float bowl and the main body of the carb. you may have one in the front and one in the back depending on the carb.

Thanks Gary. It's an AED Holley 750dp. So, either way, it's right there when I take the float bowl off correct?

Take off the secondary float bowl. Remove the secondary metering BLOCK. Power valve is on the back side of the block. If you have a metering PLATE (thinner) you don't have a power valve

Virtually all Holley 4160, 4150 style carbs have a power valve on the primary side. Some mechanical secondary carbs will have them on the secondary side too.

To only have one on the secondary side would be something some one had been messing with.

Just because it has a secondary metering block instead of a plate,doesn't mean there is a power valve there. My 750 dpl pump mech secondary carb has the power valve blocked off in the back. That said it may not have come that way from the factory but i believe it did.

On your 750 its between the primary metering block and the main body.

The reason Holley put PV's on the secondary side of some large double pumpers is because it allows them to reduce the secondary jets about 8 sizes. Without the PV the jets are so large that under heavy braking the fuel in the bowl would push its way up the passages and out the boosters which could stall the engine. The smaller jets minimize the "window" but with the powervalve open, the total fuel metering is the same.

Think about how a PV works. Stays closed until vacuum drops below its rating. The secondary main metering system opens only when the secondaries are open. I cannot think of a situation where you would have the throttle opened far enough that the secondary butterflies open but still have enough manifold vacuum to keep the PV closed.

"The reason Holley put PV's on the secondary side of some large double pumpers is because it allows them to reduce the secondary jets about 8 sizes. Without the PV the jets are so large that under heavy braking the fuel in the bowl would push its way up the passages and out the boosters which could stall the engine. The smaller jets minimize the "window"."


Hey that's great info right there, i have that problem on mine under heavy braking it tries to stall, i'm gonna try dropping the jet size and adding a PV to the back. Thanks.

You will have to obtain a secondary metering block thats machined to accept a PV.

Mine already is, the power valve is blocked off.

http://www.holley.com/data/TechService/Technical/4150-4160%20Exploded%20View.pdf

ref #s 121 and 147