This manual covers the Mercury 30 and 40 horsepower EFI four-stroke outboard engines, specifically models 30 EFI FourStroke BigFoot and 40 EFI FourStroke Non-BigFoot with serial number 1C104334 and above. These engines are engineered for reliable performance in marine applications. This comprehensive guide details all aspects of maintenance, service, and repair, ensuring your outboard operates at its peak efficiency. The purpose of this manual is to provide detailed, step-by-step instructions for the complete servicing of your Mercury outboard. It includes general information, specifications, rigging details, maintenance procedures, fuel and cooling system service, engine and lower unit repair, electrical system diagnostics, bracket unit information, wiring diagrams, and troubleshooting guidance. By following the procedures outlined, owners and technicians can effectively maintain and repair the engine, ensuring its longevity and optimal functionality.