No.1 = The ide screw, This has no specific setting. just screw in until the engine idles but when in gear does not pull away. Out if its pulling.
No.2= The Idle air mix screw, The default is to lightly screw the screw all the way in and then back it out 1 1/2 turns. Once you have No.1 set you play with this to give the highest idle speed.
No.3= the Carb bowl drain screw, Use this is you think there may be water in the bowl or if you want to check theres fuel in the bowl.
You might want to give the carb a good clean, looks like theres some alum oxide/ old fuel scum behind where the petcock mounts. Pop the two screws out that hold the bowl on and clean in there with petrol/carb cleaner and take the two brass jets out and make sure there clean.
Excellent picture of the carb BTW!
85 Tri-Z "Rumble Bee"
85 250R "Red Rocket"
83 200X "Flat Tracker"