1991 Yamaha YZ250B Owner's Service Manual (P/N LIT-11626-07-56)

• Covers the 1991 Yamaha YZ250B (3XK model range), detailing specs for engine, chassis, and electrical systems
• Original OEM publication (P/N LIT-11626-07-56, 1st Edition, June 1990)
• Contains 15 high-resolution exploded-view assembly diagrams and 6 primary specification tables for accurate tuning

Structure and Diagnostics

When maintaining a vintage two-stroke competition machine, having exact factory documentation saves hours of guesswork in the workshop. This 175-page publication outlines essential operational and inspection procedures for the YZ-series. It guides technicians through detailed disassembly reviews, component inspections, and assembly data for the liquid-cooled, 2-stroke engine and multi-link monocross suspension. Please note that working on high-performance motocross bikes involves inherent risks; always depressurize systems and disconnect ignition sources before beginning component inspections.

Engine, Chassis, and Electrical Specifications

The documentation delivers precise torque values, fluid capacities, and wear tolerances critical for the 3XK-series build. For instance, it lists cylinder head warp limits at 0.03 mm and a cylinder bore standard of 68.00–68.02 mm. You will find exact fluid requirements, such as the 0.75-liter transmission oil capacity and the 570 cm³ front fork oil capacity (per unit for non-European models). Electrical diagnostics are thoroughly mapped out, noting the CDI charging coil resistance at 36–54 ohms for the second coil circuit. Fastener specifications, like the 25 Nm cylinder head nut torque, help maintain engine integrity and suspension performance. This manual acts as a reliable repair reference for factory-authorized setup parameters.