This Service Repair Manual covers the Mercury Mariner outboard engine, specifically models within the 40 / 45 / 50 / 50 Bigfoot (4-Stroke) engine family, with starting serial number 0G231123. Engineered for reliability and performance, these Mercury Mariner engines are designed to provide dependable power for a variety of boating applications. Their robust construction and advanced 4-stroke technology ensure efficient operation and longevity, making them a trusted choice for marine enthusiasts. This comprehensive manual provides detailed information essential for the maintenance, repair, and troubleshooting of your Mercury Mariner outboard. It includes in-depth coverage of the powerhead, cylinder head, cylinder block/crankcase, lubrication systems, and transmission components, including specific sections for Bigfoot and non-Bigfoot gear housings. Furthermore, the manual details maintenance procedures for the fuel system, fuel pump, and carburetor, as well as electrical systems such as charging, starting, and ignition. It also addresses controls, including throttle/shift linkage, tiller handles, power trim, and manual tilt assist, along with installation guidelines and emissions control information. This resource is designed to assist owners, technicians, and mechanics in keeping their Mercury Mariner engine in optimal condition.