Holley carb. gurus needed!

[Rev]

Originally Posted by 82 GT

Idle vacuum is between 14-15hg(Park) and I'm running a 6.5 power valve.
I'm beginning to wonder if maybe my PV is closing before the end of the run and shutting off the power circuit of the carb.
I have a vacuum gauge I'm going to hook up so I can watch it during a pass down the track.

Remember that it's when the manifold vacuum is below the rating that the power valve is open. At WOT, the vacuum is right at 0 or a hair more. No matter what pwer valve # you use, it will always be open at WOT.

Rev

[~The Jester~]

There is absolutely NO WAY I would start playing with transfer slots, and drilling holes in the butterflies until I got the idle screw issue figured out.

I'm with Brian on this one, that motor isn't going to want to idle much below 950 rpm at best, if that's where she's happy, then that's where she needs to be. You may however find that changes once you get your issue figured out.

Exactly which carb are we talking about? Some models, that screw adjusts the air/fuel mixture for the idle circuit, on other it does not. TRUST ME, read on.

On MY carb, those screws did squat for air/fuel ratio. That is determined internally, all those screws did was adjust the AMOUNT of air/fuel that got fed through the idle circuit. Yes, I learned that in the book too. heehehe

Brian, we need to make you a "book on tape" so you can listen to it on your way to work! hehehehehe

[82 GT]

Originally Posted by Rev

Remember that it's when the manifold vacuum is below the rating that the power valve is open. At WOT, the vacuum is right at 0 or a hair more. No matter what pwer valve # you use, it will always be open at WOT.

Rev

Not exactly true. Manifold vacuum WILL raise as rpms increase. I DID read that in my Holley book....LOL
According to the book, you're supposed to find a PV rating that will remain closed at idle yet high enough to stay open during acceleration periods(drag racing)
My Holley is a 750dp(4150).
Only a vacuum gauge will tell you exactly what PV you really need without the "guess" work.

[Rev]

Carbs are pretty simple if you take them circuit by circuit and undertstand how a change in one circuit might affect the other circuits. They all have to work together for the engine to run well.

Rev