New Holley wont idle down

Discussion in 'Engine Topic' started by arick793, Sep 21, 2017.

  1. arick793

    arick793 Veteran Member

    1,108
    5
    Oct 27, 2008
    Rochester, NY
    I backed the chokes fast idle adjustment all the way down just to rule it out. No change. I haven't taken the carb back off yet to see if the secondaries are cracked open at all
     
  2. arick793

    arick793 Veteran Member

    1,108
    5
    Oct 27, 2008
    Rochester, NY
    I'm brand new to carbs with 4 corner idle adjustment, so i missed the problem entirely. Apparently the secondary throttle blades are SUPPOSED to be open a bit at idle, there is a very small screw that pushes against the secondary linkage, that can only be adjusted while the carburetor is off and upside down... Well I guess it's adjusted too far in, because the engine is idling on the secondaries alone. I should be able to back that screw off a hair and have everything functioning normally again.
     
  3. 1980RS

    1980RS Veteran Member

    1,628
    18
    Jun 17, 2006
    Is this carb a VS or a DP?, if it's a DP then you can get the part for the secondary that has an idle screw on that side to close it down easier. Here is a trick I use on VS carbs for the sec. idle, I take that screw out of the baseplate and pull the diaphragm pod off and then put the screw in from the top side, makes it easier to adjust.
     
  4. 71RS6SPD

    71RS6SPD Veteran Member

    154
    4
    Nov 14, 2016
    Fix the vac leak before making any changes.

    In a normal DFDP holly carb, the secondary 'closed' throttle position should only be adjusted open based on idle requirements. The primary throttle blade position should be fixed so the proper amount of the transfer slots are showing. (A small square). This is done before installation. Then use the secondary throttle position screw (under the plate) to adjust the idle. This method worked wonders on my SBC 355 w/holly 650 DFDP.

    The idle screw should only be used for minor weather related adjustments

    All engines do not require that the secondaries be open as the primaries often supply enough flow without overexposing the transfer slots. I did need more flow so I opened the secondaries a small bit.

    If you have 4 corner idle screws I would set them all as above before install based on the transfer slots. After install, close/open the rear to reduce idle, leave the front alone. I would probably first try to set the front and rear the same based on the 4 transfer slots then use the mixture screws and timing adjustments to set the idle.
     

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