This manual covers a comprehensive range of off-road and dual-sport motorcycles manufactured between 2000 and 2007. Renowned for its 'Ready to Race' philosophy, the manufacturer has consistently produced high-performance machines, and this series of models, including the 250 EXC Racing, 400 SX, 450 SX, 520 SX, 525 SX, and their various cross-country, enduro, and supermoto variants, exemplifies this dedication. These motorcycles are characterized by their robust single-cylinder, four-stroke engines, advanced chassis designs, and sophisticated suspension systems, making them competitive across diverse terrains and disciplines. This factory service workshop repair manual provides in-depth technical information essential for the maintenance, repair, and diagnostics of these models. It covers all major vehicle systems, including detailed engine mechanics, the complete electrical system with wiring diagrams, chassis components, wheels, tires, and bodywork. The manual offers step-by-step procedures for periodic maintenance, fluid changes, component servicing, and complete disassembly and reassembly. Comprehensive troubleshooting guides and specific procedures for tasks like valve adjustments, brake system servicing, and suspension maintenance are included, making it an invaluable resource for owners and technicians alike.