car is running rich how do you lean out a Holley?

Discussion in 'Classic Mustang Specific Tech' started by 65stang289, Dec 10, 2003.


  1. 65stang289

    65stang289 New Member

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    I need help on how to lean my Holley 600 out. I know it is the two screws on the side but dont know what way to turn them. :shrug:
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  2. 68GEETEE

    68GEETEE Member

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    as far as the screws, with the engine off turn both screws clockwise until they are all the way in. Pay attention to their position and back them out two full turns. You must do both screws equal number of turns. Start the engine. From this point you can lean it by clockwise turns, or rich by counterclockwise. Again it is vital that both screws have the same number of turns. Keep in mind there are other factors that could make her run rich. Vacuum leaks come to mind.
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  3. 65stang289

    65stang289 New Member

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    My screws show about ten threads on each side they are out alot so I have to turn them both in all the way and then 2 full turns out and just keep turning it out till it runs ok.
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  4. pabear89

    pabear89 Active Member

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    Or in, I use a baseline of 1 1/2 turns out from fully closed on the mixture screws.
    A 1 turn after screw touches the throttle plate to start with.
    Adjust throttle screw till it reaches about 6-700 rpms and work the mixture screws till a smooth idle.

    PB
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  5. D.Hearne

    D.Hearne Banned

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    The two screws y'all are trying to adjust are the IDLE mixture screws. They have no effect on the mixture once you hit the gas pedal. To change this, you have to re-jet the carb. The jets are located inside the main fuel bowl.
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  6. RaSMG

    RaSMG Founding Member

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    read what d hearne said .. the screws on the side of the metering blocks are the idle adjustment screws which only effect the idle mixture .. you want to get them adjsuted to put out maximum vacuum at a given idle rpm or to maintain the highest rpm once warmed up .. that means they are adjusted properly, then adjust the idle speed to speed or slow it down. shouldnt take more than 2 full turns out on each side, usually between one and one and a half turns on a holley/demon. if its leaning out on the top end(read the plugs) then you need larger secondary jets, if its leaning out between 1000-3000 rpm under partial throttle then its the main jets .. also try different timing curves most people with carb problems just have mistuned ignitions .. and try different vacuum advance springs if the secondaries are vacuum operated.
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  7. D.Hearne

    D.Hearne Banned

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    Chances are the Holley 600 he has , will have a secondary metering plate, and not jet screws in a block.
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