I have a carter 600 afb carb and when I screw the mixture screws qll the way in or out my carb seems to take no adjustment. The motor doesnt try and die or anything. Is this normal? I took the screws completely out when it was running and the motor stayed running. I had my step dad rebuiod the carb and it works fine besides this issue.

It may still be getting fuel from somewhere. Maybe float adjustment or too much fuel pressure.

Idle speed screw set too high, bypassing the idle mixture circuit.