This manual covers the 400 SX, a competition motocross motorcycle produced from 1998 to 2005. Renowned for its robust LC4 single-cylinder engine, known for its torque and durability, and high-performance WP suspension, the 400 SX is engineered for demanding off-road use. It competed in the motocross segment against models from Yamaha, Honda, Suzuki, and Kawasaki. This generation of the 400 SX embodies a strong heritage in off-road racing, offering a pure, performance-focused riding experience.

This workshop service repair manual provides comprehensive guidance for the 400 SX, applicable across all global markets. It details essential maintenance procedures, from routine tasks like oil changes and filter replacements to advanced engine and suspension rebuilds. The manual includes in-depth coverage of the engine mechanical and electrical systems, fuel system, transmission, brakes, chassis, and wheels. Furthermore, it offers troubleshooting assistance for common issues, diagnostic flowcharts, and detailed technical specifications, enabling owners, mechanics, and technicians to effectively maintain, repair, and optimize the performance and longevity of their vehicle.