This manual covers the YZ125, a renowned motocross and off-road competition motorcycle produced between 1999 and 2006. The YZ125 is celebrated for its lightweight, agile chassis, potent 125cc two-stroke engine, and a legacy of performance and reliability that has made it a favorite among racers and enthusiasts. During its production years, this model series underwent significant refinements, including chassis geometry updates for enhanced handling, engine improvements for better power delivery through advancements in the Power Valve System (YPVS), and updated suspension components. Its engineering quality and consistent performance have earned it numerous accolades and championships in its class.

This comprehensive factory service manual provides detailed, step-by-step instructions for the diagnosis, inspection, repair, and overhaul of all major mechanical, electrical, and chassis systems. Coverage includes the engine, fuel system, cooling system, transmission, drivetrain, brakes, suspension, steering, wheels, and electrical system. The manual also details periodic maintenance procedures, troubleshooting guides for common issues, specific part numbers, and essential torque values, ensuring owners and technicians can maintain optimal performance and longevity. With over 300 pages of technical information, it serves as the definitive resource for anyone working on the YZ125 from the 1999-2006 model years.