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Old 06-29-2007, 07:29 PM
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Q-Jet idle

Hello. Newly rebuilt 350 (top and bottom), stock Q-Jet carb (also rebuilt.) Automatic tranny. (80 vette). The car starts fine, but as soon as the choke is off (butterfly wide open) the engine speed drops and stalls. I've got the idle speed screw turned almost completely in just to keep it running, but even then it still wants to die. Idle mixture screws? If so, what do I do? What else could be causing this? Any ideas would be greatly appreciated!

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Old 06-29-2007, 08:22 PM
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Could be many things. Start with the idle mix screws for now. Go all the way in, then back out about 1 1/2 turns. If this won't do it go another 1/2 turn. Adjust 1/4 turn out until you reach highest RPM. Adjust each screw equally. If you turn one, turn the other the same amount. It helps to have a vacuum guage to measure but for now, just LISTEN to the engine. See if this can get you idling for now. If the carb was properly rebuilt, you should be OK. Unless you have a vacuum leak somewhere which will also cause problems
Hope this helps,
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Old 06-29-2007, 08:32 PM
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Here is a site from the Knowledge Base on this site, It has everything you need to tune your carb,
http://www.recarbco.com/technical/
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Old 06-29-2007, 10:36 PM
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It would have to be incredibly lean for it to die after the choke comes off. Personally, I'd be looking more at vacuum leaks in the carb base gasket, large vac hose, ie: cruise hose, booster hose, PCV hose or intake gaskets too.

Mark
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Old 07-01-2007, 09:48 PM
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Does it have an idle solenoid on the driver's side front of the carb? If so, and if it's wired to control the idle speed any time the ignition is on, that's where you set the idle speed, not the "regular" idle-speed screw.
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Old 07-02-2007, 03:54 AM
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Doc here,

Check your timing..BE sure it is at LEAST Close before trying to set a curb idle..If it is too far retarded it will die at lower settings..(probably spit back too)

Then Check to be sure the primary and secondary linkages are operating properly..and not "locking the secondaries open" at idle..First clue is a really hard throttle..These can "fall" one atop another on the throttle body just by reassembling the carb and not keeping an eye on it until you have it all assembled..

Be Sure the Vacuum modulator Valve is Connected (AT both ends! Not just the manifold Both ends have a Rubber hose that rots and falls off)

Be Sure the PCV is hooked up and not open to static air..and operating properly (rattle it) ..

Be sure the power Brake Booster is connected and it's check valve is not leaking or broken..and that the booster doesn't have a major "Hiss" when the pedal is depressed.

Let us know how you make out!

Doc
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Old 07-02-2007, 07:59 AM
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I have seen one Qjet that had an internal major vacuum leak and a new kit had no effect. I talked with a lot of mechanics about that car and they have seen that too, with a few Qjets.

The mixture screws won't work right, plus you keep adjusting the idle stop screw, but it changes each time you try to idle.

On this one, if you could get it to idle, it almost sounded like a semi-hot cam, but this car was stock.
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