This manual covers the Mercury Mariner 30 Jet - 40 outboard engine, a water-cooled, 4-cylinder marine propulsion system designed for reliable performance. Featuring a jet drive transmission and likely equipped with a CDI ignition system and an alternator charging system, this engine is engineered for a variety of marine applications. Its robust construction and efficient design ensure dependable operation on the water. This comprehensive Service Repair Manual provides essential information for the do-it-yourselfer and experienced mechanic. It details maintenance procedures, troubleshooting guidance, technical specifications, and safety recommendations specific to the Mercury Mariner 30 Jet - 40. By following the instructions within this manual, owners and technicians can effectively maintain and repair the engine, ensuring its longevity and optimal performance.