This Service Repair Manual covers the Mercury Mariner JET outboard engine, a 20 horsepower water-cooled unit featuring a jet drive propulsion system. Designed for reliable performance, this engine is built with robust engineering principles to ensure dependable operation in various conditions. Its specific application is as an outboard jet drive, offering a unique propulsion solution. This manual applies to models with US serial numbers 0G044027 and above, and Belgium serial numbers 09807909 and above. The purpose of this comprehensive English-language manual is to provide detailed information for the maintenance, repair, and servicing of your Mercury Mariner JET engine. It includes essential procedures, technical specifications, troubleshooting guides, and safety recommendations. By following the instructions within this manual, owners and technicians can effectively maintain the engine's optimal performance, ensure its longevity, and address any operational issues that may arise.