I have an Evo 50 with O.S. 50 SX-H. I've never under any conditions been able to use any more than 1 turn open on the main needle. Most of the time it's about 3/4 turns open. I questioned this myself since I've been running model engines for almost 40 years and I've never had one that needed a setting like this but that's the way this engine is. What ambient temperature do you fly at? The warmer it is outside the leaner the engine has to be set. Mine is typically about 3/4 turn on a cooler day (60-70 degrees) and 1 1/4 turns when it's hot and humid.

Mike