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Thread: Idle mixture still too rich! Help!

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    Default Idle mixture still too rich! Help!

    Hi all. First time posting so thank you all in advance! Used to run an '84 Mustang with a 600 (4160) so I used to mess with these but I'm rusty. Fast forward 18ish years later and my son brings home a '72 Thunderbird with a bone-stock (read: small cam) 429 4V and 45K original miles. It's got what I understand to be a Holley 600 (LIST-7053-1) and it will only idle with the idle mixture needles seated. Here's the specs:
    Normal tune-up stuff from us, fresh oil/filter/plugs/wires.
    New battery and starter
    Advance at idle: 10°
    Full mechanical advance: 28° around 2,500 RPM.
    Side hung float bowls (not sure if it matters).
    Main Jets: 632
    Power valve: 6.5
    Choke (hot air style), not functioning but open fully.
    Engine up to temp.
    Will only idle with idle screws seated and feels like the secondary's are not coming on at all.

    Next: Fresh cleaning and full rebuild on carb with Edelbrock kit. (Thought Edelbrock kit for Holley was odd, but it's what I could get local.)
    New vacuum diaphragm on secondaries.
    Purple spring
    New 6.5 power valve
    Primary throttle plates set to show slot as a square, no more
    Secondary throttle plates set 1/2 turn off of closed (using set screw on the bottom).
    Choke and fast idle functioning (opens idle slightly more)
    bowl levels set just to edge of sight holes.
    Fuel pressure checked at 7 psi.
    Would fire but not run.

    Next: Screwed curb idle screw in another 1.5 turns so much more slot is exposed
    Runs but still will only idle with idle screws seated.

    Used the carb cleaner test to check for vacuum leaks, none
    Disconnected the PVC and plugged the port (just to be sure)
    Engine now fully up to temp and choke off.
    STILL will only idle with idle screws seated and curb screw cranked in.

    WHAT AM I MISSING?!? Any advice would be appreciated! Thanks, Brad in CT

    P.S. One think I thought was odd was that the throttle body gasket that I used from the kit was slightly larger than the barrels. Of the ones I had to pick from there were a couple that hung significantly into the barrels, one that was maybe 1/8" larger all the way around (that I used) and a couple others that were obviously too big. Could this be causing an issue?
    Last edited by SHOBrad; 09-09-2021 at 11:50 AM.

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