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Thread: BBC 540 won't idle down

  1. #1

    BBC 540 won't idle down

    This is a mild 540 with 9-1 comp. I am running a Comp thumper roller cam with 32 degrees of total timing, an Edelbrock Air Gap and a 870 street avenger. The floats are set and air screws are almost all the way out. That is where the best idle is but I can't get it below 1000 rpms. It wants to die out unless you give it a little gas.
    Any and all help would be appreciated.
    Thanks

  2. #2
    Senior Member RACING JUNKIE
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    You have an air gap in your air gap, somewhere.

    Check for vacuum leaks. New combination? Were the heads milled?
    -WJ Birmingham

    OneBadGMC.com

  3. #3
    This is a new combo. The heads were not milled. Everything is brand new.

  4. #4
    Senior Member RACING JUNKIE
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    Yep a vacumn leak is likely to blame. Had a vacumn gauge on it yet?

  5. #5
    Haven't had a gauge on it yet. That's next on my list. It seems like their is plenty of vacuum, it runs power brakes with 9" booster with no problem.

  6. #6
    Senior Member RACING JUNKIE
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    Quote Originally Posted by landon718
    Haven't had a gauge on it yet. That's next on my list. It seems like their is plenty of vacuum, it runs power brakes with 9" booster with no problem.
    That's because you have the butterflies closed and the idle needles all the way out.

    You have a leak somewhere. Set the butterflies back to factory spec and the needles at 1.5 turns out. See where your idle is then.
    -WJ Birmingham

    OneBadGMC.com

  7. #7
    Senior Member RACING JUNKIE
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    Try to completely cover the carb with your hand and see if it dies.
    If it don't die then you know you have a leak for sure...but it still could have a small one even if it does die. Maybe spray carb cleaner along the intake /head surface and see if the thing speeds up. I've also heard of people using propane to find a leak but never tried it. Could be under the carb too.

    P.S. The idle screws on a Holley metering block control fuel not air unless I am misunderstanding your post.

  8. #8
    I found that the 4 holes in the intake that are not used with aftermarket heads were leaking a little bit. Don't know why, there is nothing under the holes. I closed them up and no more leak.
    Thanks, for all the input

  9. #9
    Senior Member RACING JUNKIE
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    Glad you found it and it was simple to fix.
    -WJ Birmingham

    OneBadGMC.com


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