The Yamaha TZ125G1, produced between 1990 and 2005, represents Yamaha's commitment to high-performance racing motorcycles. As a purebred racing machine, it inherits a legacy of success from Yamaha's extensive Grand Prix experience. This model is engineered for track use, focusing on lightweight construction and responsive handling, powered by a two-stroke, single-cylinder engine. Its design prioritizes performance and rider engagement, making it a significant machine within the competitive racing community. This factory service repair manual provides comprehensive, English-language documentation for the Yamaha TZ125G1. It covers a wide array of systems, including the fuel system, cooling system, engine top-end, clutch, lubrication system, crankshaft and transmission, wheels, tires, final drive, brakes, suspension, steering, frame, and electrical system. The manual offers detailed maintenance procedures, advanced troubleshooting guides, repair instructions, diagnostics, and wiring diagrams, all presented with factory-level technical information and hundreds of detailed illustrations. This resource is essential for owners, mechanics, and technicians to ensure the proper maintenance, repair, and optimal performance of the TZ125G1.