QJet Adjustment Help
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QJet Adjustment Help - 7/18/2007 6:32:22 PM
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L82Steve
Posts: 11
Joined: 7/18/2007
Status: offline
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Tried to adjust my QJet and ran into some problems. I was adjusting the idle mixture screws and noticed that while adjusting them they had no affect on the motor. I turned them all the way in and no change, turned them almost all the way out and still no change. Isn't the motor suppose to die if you turn them all the way in? Every other car I have adjusted the idle mixture srews in made a difference in the way it ran. Can anyone tell me what kind of response I am supposed to get while adjusting them? Is it different in a corvette? What am I missing? The engine has 90K on it and I don't think the carb has ever been rebuilt. Need advise
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RE: QJet Adjustment Help - 7/18/2007 8:22:19 PM
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pg
Posts: 1044
Joined: 8/7/2006
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Hi L82Steve, I'd start by looking for vacuum leaks around the carb and manifold. PG
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RE: QJet Adjustment Help - 7/18/2007 9:55:05 PM
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L82Steve
Posts: 11
Joined: 7/18/2007
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Thanks for the reply. I've checked the carb and manifold but found nothing. Is there a certain way to check for vacuum leaks? If I have a vacuum leak would I be able to close the idle mixture screws all the way and keep the car running? When I drive the car it cuts out like it is starving are these all symptoms of a vacuum leak?
L82 Steve.
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RE: QJet Adjustment Help - 7/19/2007 3:21:46 PM
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78buckshot
Posts: 654
Joined: 1/28/2007
From: Michigan
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Hi L82Steve, it sounds like there are other issues with the carb, with the idle mixture screws all the way in it should have stalled out from too lean a mixture, the power piston may be stuck in the up position which would give you a rich mixture all the time but I don't think it would be enough to keep the engine running with the screws all the way in. You don't know the history of the carb, someone may have made some improper mods or adjustments that may be causing the trouble. I would tear the carb down completely and check for damage, if it looks good then rebuild it with a kit along with a new float and choke pull-off. Let us know what you find.
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RE: QJet Adjustment Help - 7/20/2007 11:08:55 AM
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L82Steve
Posts: 11
Joined: 7/18/2007
Status: offline
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78Buckshot,
Thanks for the reply. I don't know anything about the carb but at least this gives me a direction to go in. I'll check it out and let you know.
Thanks again
L82Steve
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RE: QJet Adjustment Help - 7/20/2007 8:20:21 PM
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73shark
Posts: 1097
Joined: 4/18/2006
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Get yourself a copy of HP Books Rochester Quadrajets. Has a lot of good info in it. Also the factory service manual has all of the settings. Sounds like a good rebuild is in order. You can check for vacuum leaks with an unlit propane torch. Just point the nozzle around the various carb and intake gaskets and hoses and listen for a change in engine speed.
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So many toys, so little time
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RE: QJet Adjustment Help - 7/21/2007 12:39:12 AM
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cwb
Posts: 1508
Joined: 5/13/2007
From: eastern NC
Status: offline
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quote:
ORIGINAL: L82Steve
If I have a vacuum leak would I be able to close the idle mixture screws all the way and keep the car running? L82 Steve.
No.
It doesn't matter if you have a vacuum leak or not. If all else is in order, and you seat the mixture screws (all the way in), it's gonna' shut down.
78 was right. And the acceleration pump might be stuck in the 'deliver' position.
Seems also, if the acceleration pump can't deliver enough fuel to keep the twister turnin', even with the mix screws seated, then the only other place the fuel is gonna' come from is the secondaries, and even then, only if they're vacuum secondaries, as opposed to mechanical.
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Don''t know nuthin''; ain''t never got paid for wrenchin''...
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