Rochester Quadrajet Carburetor Tuning
When you first start up the engine you should try to get the idle speed set to the point that the engine runs on it's own. Let the motor run for 5 minutes in order to let it warm up.
Hook a vacuum gauge to a full manifold vacuum port. A full vacuum port is any port that maintains vacuum at idle. You may also use a tachometer instead of a vacuum gauge.
Your engine should be running and somewhat warm. Adjust your idle mixture screws until you get the highest vacuum or tachometer reading. You may need a special carburetor adjusting tool .
This will increase your idle speed so you will have to adjust the idle speed back to your preferred RPM. Once you have brought the idle speed back down, you can again adjust your idle mixture screws so that you achieve the highest vacuum/tachometer reading possible.
You may have to do this several times, as the point is to get the smoothest possible idle with the highest vacuum reading at your desired idle RPM. Once you are satisfied with your vacuum and RPM readings you can go ahead and lean out the fuel mixture out a bit by turning the mixture screws out approximately 1/16 to 1/4 turn.