Idle adjust screw - Cars & Trucks

most older cars had 2 adjustments , a air screw for enrichment and throttle screw for engine idle speed, later models did away with the enrichment screw, to adjust set idle screw to 600 rpm, adjust air mixture screw to fastest rpm , reset idle screw to preferred idle speed.

Most older cars had 2 adjustments , a air screw for enrichment and throttle screw for engine idle speed, later models did away with the enrichment screw, to adjust set idle screw to 600 rpm, adjust air mixture screw to fastest rpm , reset idle screw to preferred idle speed.

Hello, It's been a long time since I have adjusted a Quadra Jet. Start the engine and bring it up to running temperature. Make sure the choke is fully off. At idle , turn the right hand idle mixture screw in until you hear or feel the engine start to miss. Back out the idle mixture screw 1/4 turn. Repeat procedure for the left hand idle mixture screw. Adjust idle speed screw to 800 RPM for auto trans in gear or 700 rpm manual trans in neutral.

are you allowing the car to warm up first before checking your adjustment screws? have you also checked the timing of your vehicle?

There will be a screw on the throttle shaft that can be used to adjust idle rpm but you should find out why the idle mixture screw is not making a difference. Check for vacuum leaks in all the lines and manifold gaskets.

It should have a base idle adjustment and could also have an idle speed control motor.
The base idle screw should be on the driver's side of the carb. You would also have a fast idle screw on the choke.

First, you shouldn't adjust the idle. If the idle isn't correct, that means there is an issue somewhere - not that the idle needs to be adjusted.

There isn't an adjustment screw. To adjust the idle, you will need to move the TPS (Throttle Position Sensor) forwards or backward. To do this, you will need to remove the tamper proof bolt and replace it with one that can be loosened and tightened.

Here are some images that might help to assist you, and let me know if you require any further assistance.


Adjust the curb idle with the engine warmed up and the choke off.




The air/fuel mixture screws should be adjusted with the engine warmed up and at normal idle speed, then turn each air/fuel mixture screw in one at a time until the engine just begins to mis-fire, then back the air/fuel mixture screw out 1-1/2 to 2 turns out a half a turn at a time until the engine idle is the smoothest. (your vehicle might have restrictor caps over the air/fuel mixture screws to limit the amount of adjustment)






The choke adjustments;






To adjust the vacuum tension pull on the choke pull-off:





Adjust the fast idle screw to the proper RPM with the engine cold and the choke on.

Remove the air cleaner to access the carburetor.
Note the right side of the carburetor where the accelerator cable is connected.
The cable is connected to the accelerator cam which is stopped by the idle set screw.
The Idle adjustment screw head is pushing down on a spring, which should help Identify the correct adjustment screw.
Be careful not to adjust the smaller mixture screws, unless you have a vacuum gage.
If your Idle is too high you may get after run or knocking. I would set the timing then adjust the idle afterwards.
I hope this helps out since I do not know if the carburetor is stock or not.

On any carburator,one screw is for the idle speed, the other the air/fuel mix.Start the engine and let it get plenty warmed up. Adjust the idle screw to make the engine run slow. Turn the air/fuel screw in until the engine starts to die then out till it starts running loady.You want the screw between these two locations. Adjust it till the engine runs the fastest. Now adjust the idle speed screw to about 1000 RPM.
I hope this helps you.