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1978 Quadrajet idle mixture adjustment?

Discussion in 'The Hokey Ass Message Board' started by atomickustom, Apr 24, 2006.

  1. atomickustom
    Joined:
    Aug 30, 2005
    Posts:
    2,670
    Location:
    Joplin, Missouri

    atomickustom Member

    The stock Quadrajet on my 1978 350 has no idle mixture adjustment screws! I didn't notice this until I'd already gone to the trouble of cleaning the carb, bolting it onto my new manifold, and adapting all my linkages, etc. It runs fine, but I'm sure I could smooth out the idle a bit more if I could rich it up just a teeny bit.
    There are just silver metal plates filling the round holes where the screws would normally be. Are these just covers? If I pry them off, will I destroy my carb, or will I find adjustment screws patiently waiting for me to adjust them?

    I DID try to search to see if this has already been covered. If it has, please just post a link to the old discussion.
    Also, I know that a 1978 Quadrajet isn't exactly "traditional" and don't need anyone to remind me. The entire running gear in my '53 Chevy is from a donor car (1978 Impala wagon = CHEAP), and I'll take "cheap" over "traditional" any day. You wouldn't believe how many parts you can use off of one good donor car!
  2. OLDSKEWL61
    Joined:
    Feb 8, 2006
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    565
    Location:
    Scranton PA

    OLDSKEWL61 Member

    There Are Just Covers I Ussally Jusy Drill A 1/8 In Hole From The Bottem Up Angle Toward The Front And Stop Before You Go Through All The Way And Drive Out The Cap With A Punch.

    Good Luck
    Rayday
  3. HEATHEN
    Joined:
    Nov 22, 2005
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    Location:
    SIDNEY, NY

    HEATHEN Member

    25 years ago, all of the parts stores sold "modification kits" that came with a hole saw to cut out the plugs, and a special adjusting tool, since the ends of the mixture screws resemble a clutch head, like '40s and '50s Chevies are held together with. Thexton made such a kit, but I don't know if they still do.
  4. Flatman
    Joined:
    Dec 20, 2005
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    Location:
    Hamilton, Ontario, Canada

    Flatman Member

    You might be able to grab the screw head with some small needle nose pliers, once you get the covers off :D
    Those Q Jets were great carbs, huge secondaries:eek:

    Flatman
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  5. 53sled
    Joined:
    Jul 5, 2005
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    Location:
    KCMO

    53sled Member

    Lisle tool and maybe Motormite sell q-jet tools with the funky end. Drill a small hole, run a screw in, pop out.
  6. atomickustom
    Joined:
    Aug 30, 2005
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    Location:
    Joplin, Missouri

    atomickustom Member

    Thanks for the info, everyone. I'll be drilling and popping soon.
  7. bigdog
    Joined:
    Oct 30, 2002
    Posts:
    366
    Location:
    West Branch, Iowa

    bigdog Member

    Those mixture screw plugs might be hardened steel- they were on the one I just did. Drill bit won't touch 'em if they are. I went and dug out the instructions for removing the plugs.

    1.invert throttle body
    2. place punch between two location marks over idle mixture plug
    3. break out throttle body to provide access to the hardened steel plug, drive plug out

    4.late models-cut 2 parallel slots on either side of the location marks using a hacksaw. slots should not exrend beyond 1/8 inch past the marks
    5. position a flat punch at a 45 degree angle between the ends of the saw marks in the throttle body, drive the punch between the slots causing the slug to break off.
    6. hold a center punch in a vertical position and drive it into the steel plug, then angle the punch 45 degrees and drive the plug out.

    Fun, huh? always loved beating on carburetor with hammers.

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