Yamaha Water Pump Impeller (KTH-50X) YJA-01154-47-02. Overview. The Yamaha YJA-01154-47-02 Water Pump Impeller (KTH-50X) is a genuine original equipment manufacturer component designed to circulate cooling water through the engine and maintain proper operating temperature. The impeller is a vital part of the water pump system, using flexible blades to draw water from the lower unit and push it through the engine's cooling passages.. A properly functioning impeller ensures continuous water circul