This document pertains to the Mercury Mariner 55 HP Marathon outboard motor, part of the Marathon Series. This gasoline-powered, water-cooled outboard motor features a carbureted fuel delivery system and a CDI ignition. Its power output is rated at 55 HP, and it utilizes an outboard gearcase with Forward, Neutral, and Reverse gears. Designed for marine propulsion, this engine is engineered for reliable performance on the water. This Workshop Service Manual provides comprehensive guidance for the repair and overhaul of the Mercury Mariner 55 HP Marathon. It covers essential maintenance procedures, technical specifications, and troubleshooting information necessary for proper upkeep. This manual is an indispensable resource for owners, mechanics, and technicians seeking to ensure the optimal performance and longevity of their Mercury Mariner outboard motor.