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Old 11-29-2012, 06:24 PM
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Pontiac 400 Q-Jet Idles Too Fast

Like the title says it idles too fast around 1100-1400 rpm, trans in neutral. Fast idle cam off, q-jet has tower drips. All vacuum lines have been disconnected and plugged at the source. I believe this to be a vacuum leak but no luck in finding it. Could the q-jet have a internal vacuum leak? If so how would I trouble shoot it?

I installed a bushing kit, rebuild kit, it has a new PCV gromit

bt

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Old 11-29-2012, 07:32 PM
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The only thing that I would suggest is to spray carb cleaner, with the engine running, around the base of the carb. If that doesn't find a vacuum leak, try at the base of each intake runner where they bolt to the heads.

Bill
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Old 11-29-2012, 08:57 PM
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Originally Posted by beertracker View Post
Like the title says it idles too fast around 1100-1400 rpm, trans in neutral. Fast idle cam off, q-jet has tower drips. All vacuum lines have been disconnected and plugged at the source. I believe this to be a vacuum leak but no luck in finding it. Could the q-jet have a internal vacuum leak? If so how would I trouble shoot it?

I installed a bushing kit, rebuild kit, it has a new PCV gromit

bt
Are you talking about the nozzles dripping? You might not have enough idle bypass air. If this is the case the idle screws will not be very responsive to turning them in or out. Remove a plug from a manifold vacuum port and see if the idle speed increases. If it does, that's a good indication it wants more idle bypass air.

Obviously the initial timing has to be high enough so the primaries aren't into the transition circuit. If you haven't sorted the timing out, do that first before adding bypass air.
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Old 11-30-2012, 12:00 AM
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Yes, I am referring to the nozzles dripping. As it is now the idle mix screws are not responsive. First, I will recheck and set the initial dist. timing to 14 degrees and second, remove a plug from the manifold as you suggest. That's a good idea about adding more idle bypass air. bt

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Are you talking about the nozzles dripping? You might not have enough idle bypass air. If this is the case the idle screws will not be very responsive to turning them in or out. Remove a plug from a manifold vacuum port and see if the idle speed increases. If it does, that's a good indication it wants more idle bypass air.

Obviously the initial timing has to be high enough so the primaries aren't into the transition circuit. If you haven't sorted the timing out, do that first before adding bypass air.
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Old 11-30-2012, 06:13 AM
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Quote:
Originally Posted by beertracker View Post
Yes, I am referring to the nozzles dripping. As it is now the idle mix screws are not responsive. First, I will recheck and set the initial dist. timing to 14 degrees and second, remove a plug from the manifold as you suggest. That's a good idea about adding more idle bypass air. bt
I'm sure you know this, but the idea in adding initial is to cause the idle speed to pick up, allowing the primaries to be closed down some, hopefully getting you out of the transition circuit. Just wanted to give an explanation for anyone finding this during a search.
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Old 01-11-2013, 12:26 AM
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I checked the carb and it's already drilled for by-pass air. Also measured vacuum and it's 20 " Hg. So can't blame this on low vacuum. Or as another used said in a PM, "Problem could be you (me)". I suppose I had that coming since I ask too many stupid questions. I am moving onto something else. Thanks to all who have helped.

bt
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Old 01-11-2013, 03:55 AM
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Hey, ain't no stupid questions except the one that didn't get asked IMHO.

Even though drilled, it might need more bypass air than is being provided- especially if you have a healthy cam. Good vacuum doesn't mean the carb isn't still trying to idle on the transfer circuit.

If you want to take another shot at this later on, just give a shout. Good luck.
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