It helps to have an optical tach and someone to check the head speed for you in a hover. My Hyper 50 powered raptor hovers with the actual carb opening being at just slightly over 1/4th. I have tached the head speed with the carb body at 1/2 open in a hover and it was over 2300. (Very sensitive at this high speed) I was thankful for carbon blades and metal head. 1/4 throttle opening gives me about 16 to 1700 rpm's. Every engine is different though and you will have to tune the throttle curve to get the head speed you are looking for.

Good luck and happy flying[8D]