1978 Toyota Corolla Carb and how it works

Engine Performance problem
1978 Toyota Corolla 4 cyl Two Wheel Drive Manual

Rebuilding my Aisan 2 bbl carb. Can get the fuel level in the sight glass to stop going to the top. How can I fix that I believe I adjusted the float right. Don't know whats going on. And what does the Idle mixture screw do? How does that work. I see where the needle sticks out under the throttle plate