ORIGINAL: Zippi
Zman39,
This is how I normally tune a gasser. Open both high and low needles to 2 to 2 1/2 turns. Fire the engine up and let it warm up. Using a tach, run the engine at full throttle and lean (close) the high needle until you get max rpm and then back it off a few hundred rpm. Now move to the low end. With the engine at idle, quickly move the throttle to full throttle. The engine may sound ok but lean the low end 1/16" and quickly move the throttle to full again and repeat this until the engine hesitates in the transition from idle to full throttle and then back it off (rich) a few hundred rpm. Now move back to the high end and repeat the process first mentioned.
Because idle needle is active all the time, and H-needle only at power settings, it is better to set the idle needle first, because at idle, ONLY the idle needle is active. Then after a few flights, adjust both needles to get the midrange right. Midrange has secondary importance, and is very much prop depending. Larger props are easier to tune for perferc midrange, because they load the engine better. Smaller props will have a snot-nosed midrange. (missing beats because of light loads)