Thread: 4-corner idle adjustment

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I would like to know the proper procedure for adjusting idle mixture on a Holley with 4-corner idle. Having just got my new vacuum gauge, I found that front left and both rear were fully closed! Fiddling around a bit brought vacuum at idle up from about 11" to 14", with a steadier reading.

Engine is Chevy 454 and cam is hydraulic roller of 218/226 at .050" with LC of 112 deg and mid-.500" lift. Carb is a Chuck Nuytten massaged Holley 750 double pumper which flows up to 890 cfm.

What should be my starting point with idle mixture screws? I thought both front screws should be about evenly open. Should I touch the rears or leave them closed? What do they do?

Thanks guys, Chris

Originally Posted by grifo7

I would like to know the proper procedure for adjusting idle mixture on a Holley with 4-corner idle. Having just got my new vacuum gauge, I found that front left and both rear were fully closed! Fiddling around a bit brought vacuum at idle up from about 11" to 14", with a steadier reading.

Engine is Chevy 454 and cam is hydraulic roller of 218/226 at .050" with LC of 112 deg and mid-.500" lift. Carb is a Chuck Nuytten massaged Holley 750 double pumper which flows up to 890 cfm.

What should be my starting point with idle mixture screws? I thought both front screws should be about evenly open. Should I touch the rears or leave them closed? What do they do?

Thanks guys, Chris

How are things across the pound?
You are one the right track.
Try for the highest vacuum like you are doing.
You could try working with the rears to see if you can get any more vacuum.
I would guess you could maybe pull a little more vacuum but not much more.