Yamaha - Impeller Water Pump Component YJA-01156-26-02. Overview. If you've been around Yamaha outboards, you already know the impeller is one of the most important maintenance parts on the motor. I've seen engines run strong one day and start overheating the next just because the impeller gave out. The Yamaha Impeller YJA-01156-26-02 is what keeps water moving through the system so everything stays cool and protected. It's a simple part, but it's the heart of the cooling system when you're out