Yamaha Jet, Main (#90) - 830-14231-18-00. Precision-Calibrated Main Jet for Yamaha Carburetors. The Yamaha - Jet, main (#90) - 830-14231-18-00 is a genuine Yamaha OEM main jet designed to deliver precise fuel flow in carbureted Yamaha engines. Built to exact factory specifications, this part ensures optimal combustion, smooth throttle response, and consistent engine performance-whether at idle or full throttle.. As a direct replacement for worn or clogged jets, this component plays a vital role