Power Valve Selection: The Definitive Answer

CRUZE 418 said

I will never understand all of the info in the previous 4 pages. Changing power valves from one extreme to another have done nothing for my six pack. 10 ins of vac at idle, 19 at 2500 rpm driving 55mph. Promax rear throttle plate, have tried both the factory metering plates and the ProMax replacements. Found one big mistake that I had made with the ProMax replacements, which started two more problems, start over. I believe that my phasing is off too, stock type mopar dist with FBO module. Testing last nite, engine is backfiring under wot now, and all that I had changed were the vac pod springs. So that is new.
It gets tiring when you think that you know or understand what is happening, but I don't, and I am not totally new to this. I haven't quit, but I am getting tired, and I didn't really want to go 4 barrell or FI TECH injection. I will continue to read and test, keep up with your results!

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One of the issues with PV timing (well two actually) is that some carbs are so rich that changing PV timing doesn’t affect anything. It is so rich that bringing it in later won’t make a difference.

The other is the opposite. You are lean enough that opening the PV sooner still doesn’t add enough fuel to make a difference.

The way I do it (and there are other ways but I’m pretty old and lazy) is I block the power valve off. Then I drive the car at a cruise so I’m on the main jet. Then I start taking main jet out of it until I get a slight lean surge at cruise. The I go up two sizes on the primary main jet and leave it alone.

Now you can put the power valve back in. Then I disconnect the secondary throttle blades and I wire them shut so they can’t open.

The I go out and mash on it real hard and I start looking at the plugs. If it’s lean, I open up the power valve channel restricters.003-.004 and go test it again. I keep opening up the PVCR’s until it’s correct at WOT.

Of course, of you are fat at WOT, then you would close up the PVCR’s a few thou until it’s cleaned up.

Then you can hook up the secondaries and test for WOT. Only change the secondary main jet to correct any issues you have.

Once you get the cruise right, you’ll find out how important it is to get the power valve open on time. The later you open it, the bigger the hole in the fuel curve you have to fill with accelerator pump shot.

It takes time to do it, but IMO it’s worth doing because the carb will reward you with incredible performance and drivability.