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Thread: Idle WAY Too High After Rebuild

  1. #1

    Default Idle WAY Too High After Rebuild

    I rebuilt my 3310-4 (780 cfm, vacuum secondaries, manual choke) with Holley's kit number HLY-37-754. I reinstalled it on my pickup, and the idle is outrageously high now. It can't lower the idle below about 2800 RPM. The curb idle screw is backed out to the point of not making contact any longer, so I can't adjust it down that way. I thought maybe I messed up setting the secondary idle screw, so I removed the carburetor and readjusted it according to Holley's specs and reinstalled the carb, but that didn't make any difference. The idle is still about 2800 RPM.

    I bought this carb new over 10 years ago, so I know for a fact it didn't have this problem before I rebuilt it.

    Any opinions about how to fix this will be appreciated.

  2. #2
    Join Date
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    Ellington, CT
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    Quote Originally Posted by roger97338 View Post
    The curb idle screw is backed out to the point of not making contact any longer, so I can't adjust it down that way.
    It's inhaling air from another source (other than the primary throttle blades). Check for vacuum leaks, such as missing vacuum caps.
    May God's Grace Bless You

    '78 BRONCO: 508" stroker, TFS heads, Dominator MPFI & DIS, cold air induction, dual 3" exhaust/Magnaflow mufflers, 100HP progressive dry direct-port NOS, A/C, Lentech Strip Terminator wide-ratio AOD, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, custom traction bars, 4" lift, 35" mud tires

  3. #3

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    I've only a small amount of vacuum connections, so I disconnected them. I disconnected and plugged the PCV port on the rear of the carb. The timed vacuum port is unused and capped, but I replaced the cap with a new one; And I had the transmission kickdown and distributor vacuum advance on the full manifold vacuum port, so I disconnected both and plugged the empty port. It ran really rough, and at an extremely high idle, although I couldn't put an exact number on it due to it running so rough. It was over 2500 RPM though. I ran a brand new vacuum hose from the full manifold vacuum port to the vacuum advance on the distributor, and it ran smooth again....at about 2800 RPM. Then, I replaced the two brand new gaskets with two other brand new gaskets (One between the intake and the 1" spacer, one between the 1" spacer and the carb.) and my results were no different. I also took the opportunity to look for burrs, dents or divots in the mating surfaces again, and didn't find any. I also checked (again) the mating surfaces with a straight-edge, and found them to be flat. Oh, I also tried starting it with the air filter housing not installed, on the off chance that something was hanging up on it. That made no difference, either.

    I'm going to try removing the one inch spacer, even though it didn't appear to be warped. And double gasket the intake to carb seal. I'm not optimistic that will make any difference.

    Everything I've read of similar problems, a vacuum leak is always the suggestion of the problem. Unfortunately, very few people that were given that advice updated their posts regarding what they found to be the problem and how they fixed it. (On all the forums I read.) It seems to me that if virtually everyone that knows carburetors is giving the same answer, it's undoubtedly the right answer. But...can we factor in human error here?

    Is there something that I could have done wrong when I had my carburetor disassembled that could cause this? An internal gasket that I missed? A piece of debris that I missed lodged someplace, holding something open or closed? Something I put in backwards, or maybe even missed completely? Could I have damaged a primary throttle blade, shaft or linkage part?

    EDIT: I couldn't remove the 1" spacer. I forgot that it was there to provide clearance for the fuel line and throttle cable.

  4. #4
    Join Date
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    Quote Originally Posted by roger97338 View Post
    Is there something that I could have done wrong when I had my carburetor disassembled that could cause this?
    Yes, I'd recheck the metering block gaskets.
    May God's Grace Bless You

    '78 BRONCO: 508" stroker, TFS heads, Dominator MPFI & DIS, cold air induction, dual 3" exhaust/Magnaflow mufflers, 100HP progressive dry direct-port NOS, A/C, Lentech Strip Terminator wide-ratio AOD, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, custom traction bars, 4" lift, 35" mud tires

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