This manual covers the Tri-Z 250, produced from 1985 to 1986. Model codes include YZ250-R for 1985 and YZ250-S for 1986. The Tri-Z 250 is a liquid-cooled, 2-stroke, 239cc three-wheel ATV, known for its performance and agility, drawing on extensive experience in motocross and racing. It features a 6-speed constant mesh transmission with a wet, multi-plate clutch and disc brakes for active safety. While specific horsepower figures vary, it typically produced around 36-40 HP. This model represents development in the three-wheel ATV market, building upon its heritage in high-performance off-road vehicles. This factory service repair manual provides comprehensive information for the Tri-Z 250 (1985-1986). It details complete engine overhaul, transmission and clutch service, brake system maintenance, electrical system diagnostics including wiring diagrams, suspension servicing, fuel system repairs, and chassis work. The manual also includes general maintenance procedures, troubleshooting guides for common issues, lubrication schedules, and technical data sheets with specifications and tolerances. It is designed for technicians, mechanics, and owners, offering factory-level repair and diagnostic information to ensure the proper maintenance and repair of the vehicle.