This repair manual covers Yamaha 20BMH and 30HMH Series outboard engines. These 2-stroke, water-cooled engines feature CDI ignition and carburetor fuel induction, with lubrication systems that may be pre-mix or oil injection depending on the specific model. The 20BMH offers 20 horsepower from its 323 cc displacement, while the 30HMH provides 30 horsepower from its 496 cc displacement. Both models utilize a single-speed gearcase with Forward, Neutral, and Reverse selection. These engines are engineered for reliable performance in marine applications. This comprehensive English-language repair manual is designed to assist owners, mechanics, and technicians in maintaining and repairing their Yamaha outboard engines. It provides detailed information on scheduled maintenance, including engine oil and gear oil requirements, recommended fuel types, and specific spark plug recommendations for each model. The manual also covers technical specifications, troubleshooting guidance, and essential safety procedures to ensure the longevity and optimal performance of the 20BMH and 30HMH Series engines.