You need to look closely at the manual and make sure the tail setup is as shown. Make sure the tail blades are mounted correctly and that the tail belt is turned correctly. The tail blades should turn in the direction so the blades closest to themain mast is turning up into the main rotor. This will not fix your porblem but may help. Did you check the reversing of the gyro? Both the rudder servo and the gyro have reversing and need to be correct. The C30 tail is easy to setup, just make sure the servo is centered with no sub trim and no rudder trim on the radio. Place the rudder horn on at 90 deg to the servo body. Adust the rod of the servo mount so the tail pitch slider is in the center of its through which is the same as the arm at 90 deg to the boom. What type of gyro are you using?