Your actual needle positions will be somewhat different depending on gas/oil mix, the altitude you fly at and other factors

This is a good all around adjustment procedure for most all gas engine. It's not mine but it's what I used on my Roto35vi. RCIGN1 (Ralph Cunningham) wrote this a little while ago and he's pretty much considered the authority on gas engines, especially Zenoah.

Open both 2 turns
Start engine
Lean out high speed needle for max rpm, then back off about 200 rpm
Slowly lean low needle and try transition
Do it until no transition
Open low slightly until transition is good
Re set high, leave slightly rich

And for diagnosing the engines needle settings

Applies to ALL gassers, Walbro, Tillotson, Zama, Del Orto, Bing, etc.....................


ORIGINAL: hilleyja
If the ‘H’ needle is too lean, it may cause the following three symptoms.
1. Engine stops at full throttle.
2. Engine hesitates when accelerated rapidly.
3. The engine will not come up to full RPM at full throttle.

If the ‘H’ needle is too rich, it may cause insufficient RPM at full throttle. This
causes carbon buildup on the spark plug.

If the ‘L’ needle is too lean, it may cause the following three symptoms:
1. The engine hesitates when accelerated rapidly.
2. The RPM increases at idling.
3. The engine stops when the throttle is moved from high to low.

If the ‘L’ needle is too rich, the idle may be unstable.
The position of the ‘H’ needle will vary according to air temperature and
field elevation.