A common cause too , not to be over looked, is that the the gyro may be reversed. If you so much as give a lil rudder/rotation the heli will spin fast and out of contol...consequently giving it opposit control to counteract it will send it in a furious spin the other direction. Even if you jus' tilt the heli using the ailerons will coz the gyro to react by sending the heli into a spin in the same direction.

What kind of heli are you flying???...I know for a fact that the Hummingbird CP has that problem. The instructions have you mounting the gyro incorrectly. (Flaw in the documentation).