Yamaha Injection Pump Assembly YA2-28631-20-10. Overview. The Yamaha Injection Pump Assembly YA2-28631-20-10 is a genuine original equipment manufacturer component designed to deliver precise fuel injection for optimal engine performance. This assembly plays a critical role in regulating fuel flow and pressure, ensuring the engine receives the correct amount of fuel for efficient combustion and smooth operation.. A properly functioning injection pump is essential for maintaining engine power, fu