Materials needed:
Flat Screwdriver for turning out the adjustment screws
Vacuum gauge for reading intake manifold vacuum Keep in mind as you read this article that about 1 1/2 turns out on each screw seems to work best for most people. The 'easiest' way to do it is to buy a vacuum gauge. 1) Uplug the vacuum advance and plug it off using a small screw or a hose block off. Just make sure that the hose isn't able to suck air in. 2) Hook up the vacuum gauge to the carb where you just unhooked the vacuum advance. 3) Turn BOTH idle mixture screws all the way in and then turn them less than one turn out. 4) Set your idle stop screw to the RPM's where you like (about 700rpm) and then start to turn ONE idle mixture screw out. It doesn't matter which one you do as you'll be doing this same process for each mixture screw. Watch the gauge while you turn the screw. When the vacuum gauge stops increasing, stop turning the screw and turn it back IN just slightly. 5) At this point the idle will most likely be high, so you'll need to set reset the idle again to the RPM that you like (around 700rpm). 6) After the idle is set again turn the OTHER idle mixture screw out. Watch the vacuum gauge while you turn it. When it stops increasing in vacuum, stop turning the mixture screw. Turn it back IN just slightly, maybe an 1/16th of a turn. 7) Now you're idle mixtures are set but you're idle is most likely gonna be high again! Set you're idle back to where you like and presto, you're done!! A little "fine tuning" is all that's needed now!! Remember that both idle screws don't necessarily have to be in the exact same position either. The end result of this should give you about 1 1/2 to 2 turns total on each screw from all the way in to the set position. This of course will depend on your application! Reproduced with permission from GMperformance.org | 
