This manual covers the Yamaha 4SD Outboard, a 1990 model year marine engine. Designed for reliable performance on the water, this outboard engine features a 4-stroke configuration and a water-cooled system. Its robust engineering ensures dependable operation for various boating applications. The outboard lower unit is equipped with standard Forward, Neutral, and Reverse gears, providing essential maneuverability for any vessel. This comprehensive Service Repair Maintenance Manual in English provides detailed instructions for the disassembly, repair, assembly, and inspection of the Yamaha 4SD Outboard. It includes exploded diagrams to aid in understanding component relationships and detailed procedures for scheduled maintenance, lubrication, and tune-up specifications. This resource is essential for owners and technicians seeking to maintain the optimal performance and longevity of their 1990 Yamaha 4SD Outboard engine.