The KX85 and KX100 are performance-oriented, liquid-cooled, two-stroke single-cylinder dirt bikes designed for motocross and off-road competition. Produced from 2001 to 2010, these models are renowned for their lightweight construction, powerful engines, and agile handling, making them ideal for youth riders and aspiring racers. The KX85 is available in both Big Wheel and Small Wheel configurations to accommodate different rider sizes, while the KX100 offers a slightly larger displacement for increased performance. The long-standing legacy in off-road racing is evident in the engineering and capabilities of these machines, which have consistently proven competitive in their class. This service manual provides comprehensive guidance for the maintenance, repair, and troubleshooting of the KX85 and KX100 models from 2001 to 2010. It covers all essential systems, including the engine, transmission, chassis, braking, and electrical components, with detailed procedures for routine maintenance, engine rebuilds, suspension adjustments, and carburetor tuning. The manual includes factory-authorized specifications, diagnostic flowcharts, and essential information on common wear items and potential issues, empowering owners, mechanics, and technicians to keep these high-performance dirt bikes in optimal condition for racing and recreational use.