how to adjust high idle Holley (electric choke)

Discussion in 'Classic Mustang Specific Tech' started by grantur01, Apr 11, 2008.


  1. grantur01

    grantur01 Founding Member

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    Hey guys,

    I've never messed with a carb before as I am a modular guy (01 GT). My father's 66 fastback has a holley 600 with an electric choke that was installed before we got it.

    When the engine is cold it idles soo high. The tach doesn't work in the car yet so I'm not sure but it has to be over 2k easy while its idling cold.

    Now the idle screw is adjusted just perfect so it doesn't die, but it low enough for a good choppy idle. I don't want to adjust that. There is a way to adjust the "high idle", correct? I'm looking around for a holley 600 diagram but not coming up with anything.

    My dad was talking to a guy that said the adjustment screw was underneath the holley and so the carb would have to be taken off. Is that accurate? Anybody have a pic perhaps?
  2. BarnStang

    BarnStang Founding Member

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    Not under it. The secondary stop is underneth. Look at the front of the carb. On he passenger side of the carb you should a red or black plastic bob weight. The adjustment is from the rear. Small screwdriver from the back will adjust a screw that rides the steps on this bob weight. Back the screw out a quarter turn at a time. You can pull the ground wire off the electric choke to keep it from opening until you get it set. This adjustment can be a pain to get to. Don't forget to put the ground back on when you are happy with the fast idle.
  3. TOM B

    TOM B New Member

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    The high idle screw and bump cam is on the passenger side of carb, behind the electric choke assembly. The screw is a little hard to get to unless you have a aftermarket manifold then its a not to bad. When setting the choke idle start on the highest bump on the cam, set the desired idle speed when cold. You can turn the black case to set the temp that you normally start the car, you dont need full choke when it 70 or above degrees. remember that when you turn the key on, the electic choke coil is heating up fast so you might want to pull off the wire.
    I use a real short screw-driver or make one to adjust the screw or sometimes even a needle-nose pliers. I never had to take the carb off, and or how would you adjust the RPM's anyhow.:shrug:
  4. grantur01

    grantur01 Founding Member

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    awesome! thanks for the quick replies guys

    I'm going to my folks tomorrow to chech out his harmonic balancer. He's complaining about a small vibration at low speeds. I'll check out the bump cam/bob weight. lol! I love terminology.... no not really :lol:
  5. woodsnake

    woodsnake Active Member

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  6. grantur01

    grantur01 Founding Member

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    well that was fairly easy. My stubby screwdriver wasn't short enough so I grabbed a generic cheap shorty and ripped the handle off. Then I snapped some vice grips around the shaft and turned it about 1/2 turn overall. Definately came down on idle when cold. when it was heating up though the car kept trying to die so I turned the idle screw up 3/4 of a turn. Seems to be okay now. I'm going to let it cool down and start it up again to make sure it is all good. Not sure what the fast idle has to do when the car is warmed up but it definately affected the low idle.

    Thanks guys! Your always coming through.
  7. keithnra

    keithnra Member

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    i finally learned how to do this
  8. PoppyMod

    PoppyMod Member

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    Hi,
    The fast idle cam and adjustment mechanism, along with the choke system are only operational when the engine is cold. As the engine warms, the choke bi-metal spring act's on the fast idle cam, in such away, as to reduce the RPMs to your normal curb idle speed. If really interested in tinkering with these old classics, there are many articles and books dedicated to carb specific models. Carbs can be very intimidating until you begin learning about their systems and how they function.
    BTW, buy an engine vacuum gauge and learn how to tune their curb idle mixture settings and learn about an engine's over all health.
    Happy Motoring!
  9. Michael Green

    Michael Green New Member

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    I combined several of the above suggestions into a procedure that is far easier than any of the above.

    Turn the engine off and remove the electric choke wire. Remove the spring holding the throttle closed. Place the spring near the front top of the throttle linkage forcing the throttle to wide open. This forces the fast idle adjustment screw to be pointed straight down where it is easy to reach. The attached picture shows what the fast idle screw looks like in its normal position.

    Rest a mirror on the manifold pointed upward so you can see the fast idle adjustment screw. Use an open-end 1/4” wrench and using the mirror place the wrench over the screw. (Nothing else fits with the mirror in place). Move the wrench toward the rear of the car to reduce the fast idle, toward the front of the car to increase the fast idle. Re-attach the throttle spring to the correct position and start the engine. Run for at least 30 seconds to determine if the fast idle is correct. Since the electric choke is detached, the procedure can be repeated several times until you are happy with the fast idle speed. Re-attach the electric choke and let the car run until the choke is fully open. Then adjust the normal idle screw within the throttle linkage.

    Attached Files:

  10. WTFO

    WTFO Member

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    Check out Holley's website. They have more info that you could possibly need. Did the car just start doing the high idle thing or has it always been that way since you've had it? You might want to re-check the timing first before messing with the choke system as the choke rarely goes out of adjustment (factory set). make sure the timing is correct then adjust your mix screws and finally your curb idle. After that, if it's still not right, mess with the choke.
  11. 7991LXnSHO

    7991LXnSHO Active Member

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