How do you adjust a 1barrel carburetor on 1966 mustang?

The 1 bbl carb has 2 adjustments. The one by the accelerator linkage is for the idle control. The small one on the base plate is for air fuel adjustment. With the engine off turn the air fuel adjustment screw in until it stops. Do not tighten it only until it stops. Then back it out 1 to 1 and 1/2 turns out. That will get you a good starting point. Start the engine and adjust the air fuel screw in until the engine slows down. Then turn it out until it smooths out. That will get you close. Then adjust the Idle screw for the idle you want.