BBC 540 won't idle down

Old 06-03-2008, 09:46 AM
  #1  
landon718
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Default 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
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Old 06-03-2008, 09:57 AM
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OneBadGMC
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You have an air gap in your air gap, somewhere.

Check for vacuum leaks. New combination? Were the heads milled?
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Old 06-03-2008, 02:39 PM
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landon718
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This is a new combo. The heads were not milled. Everything is brand new.
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Old 06-03-2008, 03:31 PM
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Scooterz
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Yep a vacumn leak is likely to blame. Had a vacumn gauge on it yet?
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Old 06-03-2008, 05:58 PM
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landon718
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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.
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Old 06-03-2008, 06:49 PM
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OneBadGMC
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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.
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Old 06-06-2008, 04:38 AM
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Tod74
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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.
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Old 06-11-2008, 05:44 PM
  #8  
landon718
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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
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Old 06-11-2008, 05:56 PM
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OneBadGMC
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Glad you found it and it was simple to fix.
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