I guess I have the same interest in learning how to tune an engine using the high and low end needles.

In my specific situation, I have an OS .46AX. It does very well when you open it up all the way to full throttle - revs up nicely and not much exhaust smoke. However, when you bring it down to idle, it dies. I have to keep a little extra throttle to keep it from dying.

So is this why they call them the low and high end needles? The high end is used for adjusting with the throttle wide open and the low end needle to adjust near idle?

How about rich vs. lean? Does "rich" mean there is a greater amount of fuel mixed with the same amount of air, and "lean" mean relatively less fuel for the same amount of air?