How many tail blades have you broken? Or has the tail motor been stalled at all, like hung up on something? The tail motor doesn't take any overloading very well, and the 3in1 won't take any, especially on the main motor.
If you run your AXE on a smooth surface (so it can yaw with rudder input), as you throttle up (just get it light, but still on the ground), try and yaw the AXE right (against rotor torque), does it have the power to do so? Does it take alot of right input? Does it react slowly, or respond instantly? If it doesn't respond well or takes alot of right input to get the tail to swing, you could have a weak tail motor. It's not making enough RPM's to overcome the main rotor torque, a stock tail motor runs at 16,000 to 20,000 rpm at 7.8vdc, not driving the tail gear (no-load).

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