120 MerCruiser Troubleshooting

A clogged carburetor in a 120 MerCruiser can be fixed with some basic troubleshooting.

The 120 horsepower MerCruiser is a type of outboard motor manufactured by Mercury Marine. These engines can develop problems that can often be resolved with a little time and troubleshooting.

Engine Knock

A 120 MerCruiser engine that knocks or makes a clunking noise may be suffering from worn or broken gear teeth. To troubleshoot this problem, remove the top plate from the engine's outdrive and inspect the gear teeth in the top gear set for wear or damage, then make the necessary replacements.

Engine Dies During Idling

If your 120 MerCruiser engine dies while idling, you may have a clogged carburetor. Carburetors in 120 MerCruisers can clog due to contaminants from stale fuel left in the system over the winter or during long periods of none-use. To remedy this, spray the carburetor with carb cleaner to clear out the sediment.

Intermittent Engine Problems

A 120 MerCruiser engine that starts, fails, then starts up again after a short period of time may be the result of an overheated engine coil. When this happens, you should first test the voltage across the coil with an ohmmeter. If you have in excess of 10 volts, your coil is overheating and should be replaced.

References

• iBoats.com: MerCruiser Marine Engines
• Sterndrives.com: Mercruiser Sterndrive Information
• "Operation and Maintanenace Manual Models 120 140 MerCruiser Stern Drive"; Mercury Marine; 1981

Resources

• "MerCruiser - All Gasoline Engines/Drives, 2001-2008 "; Seloc Marine Manuals; 2006