Engine slow to return to idle - Team Camaro Tech
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post #1 of 9 (permalink) Old Feb 7th, 07, 01:34 AM Thread Starter
Mick
 
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Engine slow to return to idle

Hi, my engine is slow to return to idle after opening throttle, I have checked cable(disconnected off carb) for binding,spring etc . Been over with wd40 looked for vaccum leaks.

Recently installed new super victor(old team g machined to much & was pulling in oil into inlet ports) , But was slow before i changed the manifold.

Carb is 750 aed dp,has holes drilled in butterflies( to help idle air flow without being above transfer slots???). I have opened up secondary idle screw to be able to close primary down back on transfer slot & redone mixtures to fix the problem of being so rich at idle. But ever since i have had the car it has had the "slow to return problem".

Also because of big cam, vaccum is low approx 3.5 at idle, it has 4.5 power valve can this be a problem?? if power valve isn't closed at idle could this be the problem ?
Cheers Mick
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post #2 of 9 (permalink) Old Feb 7th, 07, 01:40 AM
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Re: Engine slow to return to idle

Could very well be PV. Might have to go to 2.5. I had a problem with mine that I did not find till I put a timing light on it. Timing was not returning at idle. Ended up weights were sticking in dist. Might want to pull cap and rotor and check springs and make sure mech advance is retuning closed at idle.

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post #3 of 9 (permalink) Old Feb 7th, 07, 04:21 AM
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Re: Engine slow to return to idle

You might find the power valve is closed at any rpm above 1500 when checking with a vacuum gauge.

Low idle vacuum will go higher numerally when throttle plates are open further. However, as suggested by max, a 4.5 PV could be staying open when vacuum is approaching idle, if idle is actually 3.5 in./Hg.

Your inspection of advance springs should also include the tension of them, this can be done with a timing light. Too weak of a spring could bring advance in too quickly or all the time and make running annoying.

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post #4 of 9 (permalink) Old Feb 7th, 07, 12:35 PM
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Re: Engine slow to return to idle

Are you running vacuum advance? If so, I'll bet your VA is still "in" as RPM's are reduced. Temporarily disonnect it and see if the problem goes away (and plug the vacuum source). If this fixes the prob, get back to us,..we'll tell you how to fix the VA so it won't impact idle.

Last edited by Straight-line-69; Feb 7th, 07 at 11:31 PM.
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post #5 of 9 (permalink) Old Feb 7th, 07, 12:50 PM
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Re: Engine slow to return to idle

Internal vacuum leak under manifold, idling on the timing curve, bad vacuum advance, sticking dist weights, bad needle and seat and or float adjustment all come to mind. Power valve wouldn't cause this IMO even if blown. Holes in throttle blades I don't like but wouldn't cause this. Something plugged in the carb, maybe time for a rebuild and maybe your cam timing is is causing some form of reversion (valve adjustment? stuck valves?) where the intake and exhaust are open and the exhaust pulls fuel into the cyl even though the throttle is closed.

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post #6 of 9 (permalink) Old Feb 7th, 07, 12:58 PM
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Re: Engine slow to return to idle

Is that your white rag-top Dennis??? That's one sick '69!
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post #7 of 9 (permalink) Old Feb 7th, 07, 01:45 PM
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Re: Engine slow to return to idle

thanks dubs, much appreciated...

...Dennis

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post #8 of 9 (permalink) Old Feb 7th, 07, 03:26 PM
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Re: Engine slow to return to idle

Possible lean idle condition. Happens alot with big cams. Riching up the idle fuel mixture scews and see if the condition goes away. Doug
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post #9 of 9 (permalink) Old Feb 10th, 07, 03:45 AM Thread Starter
Mick
 
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Re: Engine slow to return to idle

Tryed heavy springs today, still the same,so i think its more like a carby problem.
No vac advance to worry about.
Will try mixtures 2 moro & 2.5 pv
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