Quadrajet Idle Speed Screw Questions

[MrSony]

Hello all. Straight to the point: car runs and drives perfectly fine. Starts fine, idles at 1000-1100 in park when warm and 6-700 in gear when warm. Reaches operating temp, oil temp, all the good stuff. The question I have pertains to the idle speed screw on the lower driver's side of the carb. Mine can be backed all the way out, so far as it is not touching anything anymore, and the engine still idles at 1000 rpm. Is this normal? I can back the idle screw off and pull forward on the linkage and make it touch the backed out screw and the idle will go down. Carb works fine otherwise. Any ideas? I have all the linkage I can pilfer from other carbs I have, but I'd rather not take it apart if I don't have too.

 

[pontiacgp]

The fast idle is sticking

 

[ed1948]

OP - once you manually pull the idle down will it stay at 6-700?
Try to manually excercise the linkage(hot engine, engine off) because it could be sticky due to wear or crud. I know WD40 is not the ideal oil to use but you could try to spray all carb linkages - cleans and is a temp lube. Also there could be wear in the throttle shaft bushings allowing air leak or binding of the throttle. When the rpms stay low just check if you have a bit of slack in the throttle cable.
Hey, I'm just throwin' out ideas against the wall in the hope one of them sticks.

 

[techg8]

Good suggestions above.

1- I have seen situations where the throttle blades get misaligned in the baseplate and don't seal all the way. This can cause the condition you describe.

2- Also, a twisted throttle shaft can allow one blade to close all the way and not the other. when you apply more force it closes the other blade. another possibile cause of your symptom.

3- Another thing comes to my mind. I see youre running a buick 350, so no computer.

what carb number are you running? It "might" have too much idle air bypass for your engine.

Idle air bypass allows air to pass through the carb body and baseplate without passing the venturis. This allows idle to be maintained with relatively less throttle opening, thus reducing the chances of primary nozzle drip. This is especially relevant on big block engines (and thus is found in their carbs), and large camshaft applications.

4- lastly, I have seen situations where the primary->secondary link that joins the two throttle shafts is misadjusted to a point where it holds the primary throttle open too far at rest.

 

[MrSony]

The carb is from a buick 350, 1978 to be exact. 17058241. The linkage isn't bound up as far as i can tell. its as responsive and free moving as it needs to be.

 

[MrSony]

OP - once you manually pull the idle down will it stay at 6-700?
Try to manually excercise the linkage(hot engine, engine off) because it could be sticky due to wear or crud. I know WD40 is not the ideal oil to use but you could try to spray all carb linkages - cleans and is a temp lube. Also there could be wear in the throttle shaft bushings allowing air leak or binding of the throttle. When the rpms stay low just check if you have a bit of slack in the throttle cable.
Hey, I'm just throwin' out ideas against the wall in the hope one of them sticks.

It does not stay at the 8-900 rpm I want it to idle at in park. I can pull back on the throttle arm, towards the front of the car, and the idle will drop (with the idle screw backed all the way out, almost to the point of it falling out) but the linkage mechanically will not allow it to close further. I looked up a video and there is an idle screw under the choke housing. I'm gonna mess with that and get back to this thread soon.

 

[oldsmobile joe]

another suggestion is to check your ignition timing. incorrect timing, too much, can affect your idle speed. incorrect base timing, stuck weights, vacuum advance incorrectly hooked up, etc.

 

[pontiacgp]

have you made sure the high idle steps for the choke are in the lower position and not stuck in upper positions causing the hi idle.

 

[pontiacgp]

The choke on that carb is supposed to be a hot air choke. I would read up on the carb before making any adjustments trying to chase down a problem. You might change something that is adjusted properly and end up causing more problems.

 

[ed1948]

Vacuum leak? pull vacuum hoses off the carb one by one and place finger over port
-brake booster check valve or brake booster itself
-carb body screws or mounting bolts loose
-seized vacuum advance on dist