This manual covers the motocross competition motorcycles manufactured between 1999 and 2002. These models, identified by chassis codes KX125-K1, KX125-K2, KX125-K3 for the 125cc and KX250-K1, KX250-K2, KX250-K3 for the 250cc, represent a significant era in motocross technology. They are engineered for peak performance on the track, featuring liquid-cooled, two-stroke engines with an Integrated Power Valve System for enhanced power delivery across the rev range. The KX series is renowned for its competitive edge, strong heritage in racing, and robust construction designed to withstand the rigors of off-road competition, making them a popular choice for enthusiasts and professional racers alike. This comprehensive Service Repair Manual provides detailed information essential for the maintenance, troubleshooting, and repair of your KX125 or KX250. It covers a complete range of procedures, from routine maintenance tasks such as oil changes and filter cleaning to in-depth engine and chassis overhauls. The manual includes extensive guidance on all major systems, including the engine, fuel system, transmission, suspension, brakes, and electrical components, supported by numerous diagrams and illustrations. With this resource, owners and technicians can confidently perform all necessary work to keep these high-performance machines in optimal condition, ensuring reliability and peak performance on and off the track.