Thinking more about this and I have a simple visual that proves out my latter description.
What would happen if you screw the air mixture screw all the way in? Yep, that's right boys and girls. The only thing going in now would be gas! In essence, by unscrewing the air mixture screw (from bottomed out), you are leaning the circuit. If you are sitting at 2 turns out and unscrew it more, you are further leaning the circuit!.
Think about it.....
