8 thoughts on “How To Adjust The Secondary Speed Screw On Holley Carbs

  1. I replaced my screw with one from Lowes that I can use a small Allen wrench to adjust so that I don't have to remove the carb to adjust secondary throttle plate opening. An Allen wrench will clear my performer intake whereas a flathead screw driver won't. I believe the size was either 8-32 or 10-32 but a package of two cost less than one dollar.

  2. I have a doubt, To open the 2ndy speed screw is in CLOCK WISE fashion? How much is a "little"? in the video is about 1 round… I have a camshaft with duration 230/230 at 050 lift, advertised 280/280 with rocker arms 1.6 ratio in a Ford 289 modified to the top I could, In your experience, about how much do I have to open this screw?
    Looks very unpleasant to remove the carburetor until 1 finds the proper opening, I hope you respond

  3. Do not forget on small engines like my 2.3l with the 390.  I have to close this to slow down the idle.  I have the idle screw back all the way out and still idles above 1000rpm.  No air leaks etc.

  4. Its all about the T-slot. I set the T-slot on the primary for .020" +/- than use the secondary to raise the idle. Then re-adjust the mixture screws.

  5. What if after making this adjustment you still have to increase the front idle speed so much that your ported vacumn is getting manifold vacumn at idle. Do you recomend drilling the throttle blades to allow the idle speed screw to be backed off?.This is a old holley trick I learned yrs ago. Wondering if this is still the fix or if theres a new way around this now.

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