might be better to ask this q over in the esky forum, but if the heli has flybar weights, move them in a bit at a time, don't move them all the way to start with, because you could have an out of control heli. Also make sure the servo's are in the outermost hole, but again make small adjustments to start with. Another thing is does it have a hiller head, or a bell hiller head? If it's hiller you can increase the responsiveness by changing to bell hiller.

If that doesn't do it, you'll probably want to check out your over all setup of the heli, ie no binding, flat paddle bars, good head speed, proper belt tension, that your motor isn't on it's way out, that your servo's are working properly and can handle the full load. Also there are some knobs that adjust the pitch and the motor throttle, those might also have to be adjusted, but I don't know what good settings are for them.

Anyways the esky forum is over here
http://www.rcuniverse.com/forum/forumid_481/tt.htm