[Formulajones]

Originally Posted by PunchT37

Remember, the power valve doesn`t richen the idle circuit.

Correct, very common misconception.

Power valve will not dump fuel until the transfer slot is open triggering the main circuit. So as long as your throttle blades are adjusted properly at idle, you will only be running on the idle circuit no matter what your vacuum power valve is.

[NeighborsComplaint]

Originally Posted by Formulajones

Correct, very common misconception.

Power valve will not dump fuel until the transfer slot is open triggering the main circuit. So as long as your throttle blades are adjusted properly at idle, you will only be running on the idle circuit no matter what your vacuum power valve is.

Take your power valve out sometime and let me know how the car idles. In theory, it shouldn't matter but if your car has a long duration cam and low vacuum and you are overlapping the idle circuit to the off-idle circuit or cruise circuit, it will flood.

[Formulajones]

Originally Posted by NeighborsComplaint

Take your power valve out sometime and let me know how the car idles.

That's not exactly how it works. A leak is a different thing entirely.



The power valve needs a venturi affect (assentially what a carb is) to pull fuel from the float bowl through the power valve circuit. That circuit DOES NOT become active until 2 things happen.......the transfer slot is exposed enough to enable the main circuit, and the vacuum drops low enough to open the power valve. Period!! BOTH of those things have to happen for the power valve to become part of the fuel curve.

So in other words, if the vacuum is low enough for the power valve to open, but the throttle blades are not open enough to start the main circuit, (hence idle condtions) then you get no fuel from the power valve.

Or if the throttle blades are open enough to enable the main circuit, but the vacuum is too high for the power valve to open, (light cruise for instance) then you get no fuel from the power valve circuit.


This power valve flooding an engine at idle has been a long time misconception that has unfortunately grown since the internet and lead people down the wrong path of carb tuning. Those that experience this issue obviously either have their transition slot too far exposed, or had a leaky power valve with a cracked diaphram or gasket problem and just blamed the power valve vacuum reading.

The correct way to tune these things is to have the power valve fairly close to idle vacuum. A couple inches is fine. It doesn't have to be half of the vacuum reading that is so commonly thrown around. All that does is cause lean stumbles right off idle and light tip in drivability problems, and then people get all crazy with pump shot trying to cover it.

[PunchT37]

Originally Posted by Formulajones

Correct, very common misconception.

Power valve will not dump fuel until the transfer slot is open triggering the main circuit. So as long as your throttle blades are adjusted properly at idle, you will only be running on the idle circuit no matter what your vacuum power valve is.

I used to run a high overlap cam with a 1000 HP. It had 6.5 idle vac in park and 5.5 in drive. The carb had a 6.5 power valve in front. Blocked in back. No problems with loading up at idle.

This thing had a lean spot deeper into the primary circuit. So, I started the power circuit ,earlier , before the secondaries. Problem solved.