I'll try to explain....
The screw on the left (pass) side is the fast idle screw. This comes into play when the choke plate is closed, its linkage pulls in a cam and this screw rides on the cam. To set fast idle, allow the engine to come to complete oper temp. Shut engine off, open throttle part way, manually close choke with finger, close throttle, release choke plate, choke plate should go open since engine is warm.
Start engine and set fast idle rpm by adjusting this screw, say 1400-1600 rpm?
The screw on the right (driver) side? There might be two - one on the carb body. This sets curb idle or base idle with no load or accessories turned on, usually set for 650-850? Whatever the book would suggest.
The other screw - directly in front of the throttle cable. It would be part of a solenoid(?) and would come into play when the A/C is turned on. With this load on the engine, the rpm drops, solenoid kicks out, thereby raising the engine rpm back to the same, if not alittle more than no A/C rpm.
Hope this helps.... Stay warm!!!
Everett "OBJECTS IN THE MIRROR APPEAR QUICKLY UPON RAPID DECELERATION"