The Yamaha TZ125G1 is a competition motorcycle renowned for its performance and racing heritage. Produced between 1990 and 2005, this model embodies Yamaha's dedication to engineering excellence in the 125cc class. Known for its liquid-cooled, 2-stroke, single-cylinder engine, the TZ125G1 has been a successful platform for privateers and factory efforts alike, consistently achieving victories in racing series worldwide. Its robust twin-spar aluminum frame, powerful hydraulic disc brakes, and responsive handling make it a formidable machine for aspiring racers and experienced competitors. This workshop service repair manual provides comprehensive, factory-level detail for the Yamaha TZ125G1, covering the production years from 1990 to 2005. It is designed to assist owners, mechanics, and technicians in maintaining and repairing the motorcycle. The manual includes detailed procedures for engine disassembly and assembly, transmission and clutch service, chassis and suspension maintenance, brake system repairs, and electrical system diagnostics. It also covers routine maintenance, troubleshooting common issues, and advanced tuning for optimal racing performance, offering invaluable guidance for all aspects of the vehicle's upkeep.