Originally Posted by dkfuji
Check your feathering shaft like indoorheli says first. You will have to use those 2 plastic wrenches that came in the bag with your heli. If it is straight then I would check for vibration due to main blades out of balance. You should be able to spin up the heli at 100% throttle at midstick (zero pitch) and the heli should be smooth as silk. If not, balance the mains by adding some clear tape.
Heli is smooth on spin up. It starts to vibrate with higher head speed.