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Thread: Lean spot just as throttle blades open & cruising.

  1. #1

    Default Lean spot just as throttle blades open & cruising.

    Holley 80457SA 600 CFM carburetor. The car is a 1964 Nova with 250 inline 6 cylinder. The issue is most noticeable when cruising with the throttle barely open. The air/fuel ratio goes over 17:1. This engine doesn’t like anything much over 15:1, so it surges & loses power until the accelerator pump is activated by accelerating. It idles at 1000/800 in gear and 13:1 AFR. The surge doesn’t seem to improve with changes to the idle screws or primary jets. Power valve is an 8.5". Are there fixed jets I can drill out to increase fuel just off idle?

  2. #2

    Default

    Sounds like you're needing more fuel sooner since the squirters help the problem. Try using a numerically smaller power valve and see what happens. What's your idle vacuum reading?

  3. #3
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    645

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    Your idle gets its fuel from the idle discharge ports, which is controlled by your idle mixture screws. Your just off idle gets it fuel from your transfer slots. The fuel for your TS is controlled by your idle restrictor in the metering block and the idle air bleed at the top of the carb. To enrich your TS you would need to reduce the idle air bleed or increase the size of the idle restrictor. Since you do not have adjustable air bleeds, you could increase the idle restrictor. It may not take much, maybe .001". Just guessing, but your idle restrictors are probably in the .030" range. I found some small drill bits at a model shop that worked for me.

  4. #4

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    Is L the correct hole to drill out?
    Click image for larger version. 

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  5. #5
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    645

    Default

    K is the hole to drill out. The fuel comes from the main well through the hole marked L, then through the idle restrictor (K) to the idle well.

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