For 2019, Yamaha has refined its distinct rearward-slanted cylinder design for the engine. Using a compact starter motor and lightweight lithium-ion battery, the 2019 YZ250F is now equipped with electric start, and the liquid-cooled, DOHC, four-valve, fuel-injected engine features a forward-positioned straight downdraft intake with symmetrical intake and exhaust ports. Fuel is delivered by a lighter 44mm throttle body through a new 12-hole Denso injector. A new, higher-compression flat-top forged piston has a bridge-box design for additional strength with minimal weight. The piston, rings, and DLC-coated piston pin, along with the offset cylinder configuration, are all designed to reduce friction loss and contribute to quick response.