Maybe you already discovered that the stock tail rotor gear ratio of king 2 is not fast enough. It is only 1 to 3.2 (32t belt pulley and a 10t tail rotor gear).  That means when the main blade rotates 1 cycle, while the tail blade rotates 3.2 cycles.  Users are complaining that the tail is not stable and will yaw or drift when throttle up; it is because the tail blades are not generating enough wind force under this low gear ratio.