I highly recommend weighing and balancing as much as you can on any heli kit, it may not seem like much but at 2400 RPM's it can cause a high frequency vibration that can greatly interfere with gyro performance
I have recently found there is some friction in a part of the head that lets the flybar "seesaw" back and forth. It isn't a critical thing but after fixing it I found it hovered even better!
The part is circled in red in the following picture:
What you need to do is roll some 600+ grit sandpaper into a small roll/tube and lightly sand the inside outer edge of each brass fitting. If not the screws that go into the brass fittings will cause some friction! Keep test fitting the screw in each until there's no friction!