QJet Adjustment Help
 

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 srewsin 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

RE: QJet Adjustment Help
 

Hi L82Steve, I'd start by looking for vacuum leaks around the carb and manifold. PG

RE: QJet Adjustment Help
 

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 leakwould 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.

RE: QJet Adjustment Help
 

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.

RE: QJet Adjustment Help
 

78Buckshot,

Thanks for the reply. I don't know anything about the carb but at least this gives mea direction to go in. I'll check it out and let you know.

Thanks again

L82Steve

RE: QJet Adjustment Help
 

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.

RE: QJet Adjustment Help
 

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 fuelis gonna' come from is the secondaries, and even then, only if they're vacuum secondaries, as opposed to mechanical.

RE: QJet Adjustment Help
 

what rpm is it idling at,if it can idle.check rear carb butterflies and make sure they are closed.is it dripping in the carb when its idling.check curb idle screw isnt open too much,bypassing idle circuit.are there mixture limiters on the 2 screws

RE: QJet Adjustment Help
 

It idles at 900 with a slight miss. I just recently rebuilt the distributerand it runs much better then it did. I noticed that it had a slight miss so I thought I would adjust the carb and found that it doesn't adjust. When I drive the car it cuts out like it is starving for fuel when I step on it, as soon as I let off it idles fine. I have timed it to spec. It has anew fuel filter/pump,plugs,wiresand fuel line. Thanks for all the great advice. I have a few things to look at and I'll get back to you and if you can think of anything else please let me know.

Thanks again

L82Steve

RE: QJet Adjustment Help
 

Check your plug wires for firin' order?

Of course that doesn't explain the mix screws non-function tho'... That needs to be addressed irregardless.