can't adjust Idle circuit
 

I have a 4150 carb 4776, I can not adjust the idle mixture correctly on the one side, the car runs fine with the screw all the way in, when I turn out the screw the car starts to run ruff, the other side works fine, turn the screw in and the car idles down, turn it out and the car will idle down, I do have a small margin of adjustment that the car will run perfect, it’s just the one side that I can’t get the correct setting, any ideas on why? I just rebuilt this carb, soaked everything, blew out all circuits with compressed air, I don’t understand what would cause this.