Hey pronoman;
You may not have enough head speed with the 3100kv motor with a 9 tooth pinion. If I were in your shoes I would get a 11,12, 13 tooth pinions and try them on that motor.
With a 10t pinion and 140t stock gear you will only have a head speed of 2460 respectively. It will probably fly with that head speed but, the tail will be unresponsive. No authority at all. A 12t pinion will give you 2950 rpm respectively. Here is the math. Kv (3100) times voltage (11.1) = motor rpm (34410). Main gear (140) divided by pinion size (12) = gear ratio (11.66), then motor rpm (34410) divided by gear ratio (11.6) = head rpm (2951) Maybe this will help you when you need to pick a motor next time. You need to know what you want the head speed to be on a given chopper. 3000 is a good speed for the King II IMHO. Gittle