The Kawasaki KX250 has been a major force in 250 cc motocross competition since it was introduced way back in 2004. Originally co-developed with Suzuki but much modified since then, this liquid cooled single cylinder four stroke bike most recently had a major revamp ahead of the 2021 season. The bike is further revamped for 2023, including significant engine modifications.

Bore of 78.0 mm and stroke of 52.2 mm provide a displacement of 249.4 cc. The engine has double overhead camshafts operating four valves per cylinder via finger followers and is run by a sophisticated engine management system controlling CDI ignition and sequential-type fuel injection. The finger followers allow 14,500 rpm to be safely obtained from the 250 cc cylinder. The compression ratio is 14.1:1.

Engine modifications for 2023 include a narrower included valve angle and slightly smaller intake valves in conjunction with a revised piston crown form, the upshot being a much altered combustion chamber. At the same time the intake and exhaust systems have been redesigned, with the intake manifold straighter and the exhaust header significantly longer.

The engine breathes through a 44mm Keihin throttle body. It exploits a pair of fuel injectors, one in the port and one upstream, in the manifold. The upstream injector has been moved to the base of the manifold and angled more towards vertical. The ems has been remapped and of the five gear ratios, two have been revised - with a taller first and a taller second, the latter now thereby closer to third.

The 2022 engine was independently measured by Dirt Rider magazine as producing 39.5 bhp at 13,700 rpm and 18.5 ft.lb torque at 9700 rpm. Of course, for Motocross it is the shape of the power curve rather than the headline figure that counts, which is why a reduction of intake valve area is not a disadvantage. One can assume that the 2023 model scores especially in this respect.