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Thread: 4-corner idle adjustment
          
   
   

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  1. #1
    grifo7's Avatar
    grifo7 is offline CHR Member Visit my Photo Gallery
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    Car Year, Make, Model: 68 Iso Grifo 7 Liter,
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    4-corner idle adjustment

     



    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

  2. #2
    erik erikson's Avatar
    erik erikson is offline CHR Member Visit my Photo Gallery
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    Car Year, Make, Model: BLOWN 540 57 CHEVY
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    Quote 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.

  3. #3
    DennyW is offline Junior Member Visit my Photo Gallery
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    Car Year, Make, Model: catch 22
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    All 4 should be even, otherwise, with 2 closed, you wouldn't need a idle adjustment, would you ?
    Start with lightly seated, and back all 4 out 1/2 turn. If it doesn't idle, turn all 4 out another 1/2 turn. Once it idles, if you turn one 1/4 turn, turn the other 3, 1/4 turn. You with me on this ? Watch the gauge until you get the highest, and steadiest reading. If, I say if, when you adjust all 4 the same, as in 2, 3, then 4, and the idle drops, you simply turn each one back in 1/8 turn. You do this evenly until you get the best vacuum reading you can. Then, the idle circuit is balanced.

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