[Question] High Idle Concern
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High Idle Concern

  1. #1
    Member chuckski190's Avatar
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    Default High Idle Concern

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ID:	185188 Old School "Gale Banks" twin turbo set up. After cruise, returning to idle the RPM's stick about 2000 rpm's. Shut the engine off and re-start, the idle returns to normal. No hard re-start, quick fire-up. This doesn't happen all the time but can be dangerous. Doe's anybody have any thoughts to try? Or what to look for?
    *Note there are clamps on the intake hoses in picture #2.

    Any help would be greatly appreciated!
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    Senior Member EVILFORCE's Avatar
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    Remove cable and work linkage by hand. See if it sticks. Either a cable or throttle plate issue.
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    Ok, But why will the idle return after the engine is shut down? Sticking linkage and or plate would not change?
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    Senior Member EVILFORCE's Avatar
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    Do you have a return spring on the throttle? Also could be the secondary plates hanging. Could be a lot of things. I would start there.
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    After you have made sure both sets of throttle plates are closing properly..

    Mechanical advance issue?

    When it doesn't stick does it drop directly to idle rpm or does in kind of wander down to it?
    Last edited by SoldHondaBoughtHondo; 11-26-2012 at 03:50 PM.
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    Quote Originally Posted by SoldHondaBoughtHondo View Post
    Mechanical advance issue?
    Don't think that would make it idle at 2k. Maybe a 100 more.
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    Great Idea, but the advance is locked out. Do you think a vacuum leak would or could cause the concern? Another thing, all four idle screws can be turned closed and the engine will still idle. The carb is a 830 and I just rebuilt it. It's been my experience with vacuum leaks the idle is not good all the time. The engine will stall. This engine runs and starts awesome. I do like the idea of the throttle plates sticking, however I have a hard time with just shutting the engine down, the idle will return down.

    Thanks guys!
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    Senior Member Hass828's Avatar
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    Quote Originally Posted by chuckski190 View Post
    Great Idea, but the advance is locked out. Do you think a vacuum leak would or could cause the concern? Another thing, all four idle screws can be turned closed and the engine will still idle. The carb is a 830 and I just rebuilt it. It's been my experience with vacuum leaks the idle is not good all the time. The engine will stall. This engine runs and starts awesome. I do like the idea of the throttle plates sticking, however I have a hard time with just shutting the engine down, the idle will return down.

    Thanks guys!
    That setup will puddle fuel in the intake tract and continue to idle for quite a while with the screws ran in. Makes it really tuff to adjust the idle mixture. But it should eventually die. If it really does continue to run then its getting fuel from somewhere that it shouldnt. Bad gasket or something.
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    Quote Originally Posted by chuckski190 View Post
    Great Idea, but the advance is locked out. Do you think a vacuum leak would or could cause the concern? Another thing, all four idle screws can be turned closed and the engine will still idle. The carb is a 830 and I just rebuilt it. It's been my experience with vacuum leaks the idle is not good all the time. The engine will stall. This engine runs and starts awesome. I do like the idea of the throttle plates sticking, however I have a hard time with just shutting the engine down, the idle will return down.

    Thanks guys!
    Idle mix screws in and motor doesn't die...where is the fuel coming from to keep the motor running?
    I'm guessing it did same thing before you rebuilt it? Is the idle speed screw cranked in most of the way?
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    Senior Member EVILFORCE's Avatar
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    Sounds like a Phucked up carb. Replace it.
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    Pooling fuel. That makes sense. That explains why it doesn't want to cold start, (have to use a quick shot of starting fluid) after it sits a few days, and it will hot start every time. I guess this is why it is call "old school gale banks set up".

    Yes the idle screw is set correctly. I set it with the linkage disconnected, then connected the heim joint linkage and verified the idle.


    Mahalo's for your help guys!
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  14. #12
    Senior Member EVILFORCE's Avatar
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    Quote Originally Posted by Hass828 View Post
    That setup will puddle fuel in the intake tract and continue to idle for quite a while with the screws ran in. Makes it really tuff to adjust the idle mixture. But it should eventually die. If it really does continue to run then its getting fuel from somewhere that it shouldnt. Bad gasket or something.
    Good call Hass. Very good possibility.
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    Puddling may account for a lack of or limited effect of idle screw adjustment, but not a high idle. That would be an issue of too much air.

    Have you tried a wrap or two on the throttle with an quick intentional return to idle? Or tried to manually manipulate the throttle arm, when it occurs, to a full closed/idle position? Anything to identify or eliminate the possibility that the throttle is or is not in-fact returning to it's full idle position?
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  16. #14
    gn7
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    This is a pretty typical phenom with a carb that has the idle speed screw set far enough to bring in the transition circuit. The transition slot is a horrible idle circuit and terribly inconsistent.
    Follow along and it might make sense.
    First, your idle mixture screws are not making any noticable change in the idle. First sign!
    The transition circuit is fed by the idle fed restrictor and the idle and transition circuit go their seperate ways right at the idle mixture screw. The idle fuel goes thru the mixture screw circuit, the transition goes straight to the carb base. Both are fed by a channel that goes from the very bottom of the metering block, to the very top, where the idle bleed mixes in some air, and acts a vacuum break so the bowl doesn't empty via a siphon when you shut it off.
    You fire it up and even throttle it, and the thing idles fine and is being fed fuel STRICTLY based on vacuum strength at the transition slot. The only thing restricting the flow is the vacuum strength and the idle feed restrictor.
    When you come down off of a run, the vacuum signal can be pretty damn high and when the blades close its pulls more fuel than when you first fired it off. The idle stays high because it has the fuel to do so, because excess fuel from a high vacuum with a closed blade started the trend, and it continues until you shut it off, and start over. It will probably idle just fine on the fire up and you never touch the throttle to change anything. No return spring thing, no "bumping the throttle". You MIGHT be able to get the idle back to normal by jazzing the throttle and disrupting the transitions circuits high vac pull on the fuel supply, and that only leads you to think its a return problem.

    If you cannot effect a change in the idle with the mixture screw, you can bet your ass you're on the transition circuit, and the transition circuit is a piss poor, inconsistent means of supplying fuel to an engine for idling. Its why there is an idle circuit.



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    Last edited by gn7; 11-26-2012 at 07:25 PM.
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