Tune-ups consist of a series of inspections, adjustments and parts replacement to compensate for the normal wear and deterioration of the outboard motor. Tune-ups can be part of the regularly scheduled maintenance as prescribed by Mercury Marine. A tune-up can also be a yearly maintenance event at the time of winterization or during the spring before using the outboard. A general tune-up includes a compression test, spark plug service, water pump check, fuel system and ignition system service.
A compression test gives an indication of the condition of the basic working parts of the engine. A low or uneven compression between cylinders cannot be satisfactorily tuned. A compression problem must be corrected before continuing with the rest of a tune-up.
Remove and replace bad or corroded spark plugs. Replace spark plug if the electrode is worn or the insulator is rough, cracked, broken or blistered. Use a Mercury-recommended spark plug. Some larger models use suppression spark plugs and should be replaced with the same type.
Faulty water pumps can result in engine damage. Replace the pump impeller, seals, and gaskets.
The fuel system includes the fuel lines and filter. Inspect all fuel hoses and lines for kinks, leaks and other damage. Replace hoses that leak or are damaged. Remove the old fuel filter and replace with a new Mercury-recommend filer. If your model has a filter screen, remove and clean it.
Smaller outboard engines require replacement of breaker points and condenser. Larger engines have electronic ignitions and may only need adjustments.
Lubricate all lubrication points. Lubricate points more frequently when the outboard is used in salt water. Lubrication points are the steering cable grease fitting, swivel bracket, tilt support lever, title tube, tiller handle and the steering link rod pivot-points.
Drain and change gear case lubricant. Check lubricant for a milky color that may be cause by water in the lubricant. Also check for metal particles. A small amount of particles indicates normal wear. A large amount of particles or water in the lubricant will mean the gear case will need to be examined by an authorized mechanic.
