Yamaha RXS 100 100cc Inlet Power Box YEIS Boost Tank 1985-1996 OEM 4X8-13581-00

Product Description

This is a genuine Yamaha OEM YEIS Air Induction Chamber, also known as an intake boost bottle or power box. Designed for classic Yamaha 2-stroke engines, this chamber works as a Helmholtz resonator by connecting to the intake manifold between the carburetor and reed valve assembly. It temporarily stores the fuel-air mixture when the reed valves close, then helps feed the charge back into the engine as the intake opens. This improves low-to-mid range response, reduces flat spots, and helps smooth throttle delivery. Made from fuel-resistant molded black plastic, it features factory Yamaha YEIS markings and the 4X8 casting code, with built-in mounting tabs for secure installation. Compatible Models: Yamaha RXS100 / RXS 100 — 1985–1996 Yamaha RX115 / RX 115 — 1981–2006 Yamaha RD135 / RD 135 — 1986–2000 Yamaha RX-King 135 / RX135 — 1983–2009 Also commonly adapted for custom Yamaha DT125, DT175, and RX100 2-stroke setups.