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Thread: 4175 metering block idle screw question.

  1. #1

    Default 4175 metering block idle screw question.

    OK before I start, I know just enough to be dangerous, so I need help (PLEASE). I have a 4175 (R80491) on a 75 LA 360 in my Cordoba which I've rebuilt. My problem is I can't get my Idle Jets to do anything even when they're turned all the way in. I'll give a run down on the info I can. My secondary throttle plates show the little sqaure on idle transfer, front throttle plate closed, engine is pulling 17 inHg vacuum, PV is a 6.5. The numbers on my jets are 632, Primary metering block is 34R-7235B, Secondary metering plate is 34R-9716B. I've double & triple check float levels. I have checked for vacuum leaks by spraying carb cleaner around intake and carb with no rev up during this process. I called Holley Tech support and they were no help after being on the phone for two hours with them. I'm hoping someone much smarter than me can give me some guidance. Car runs decent, but I'd just like to be able to tune it. I just want to say thanks for any input on this matter. Ron

  2. #2
    Join Date
    Jan 2010
    Brisbane, Australia


    I'd say the secondary throttle doesn't need to be open as far as you have it.
    17 inHg vacuum says you have a stock to mild cam. The primary side will have control if airflow goes through the primary side.
    Back the secondary speed off to the point of the butterflies are just open so they don't get stuck in the closed position. Gary

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