Use a voltmeter to check the battery voltage. Apply Dielectric grease to the terminal posts of the battery to keep it free of corrosion and to prevent the loss of voltage. Wash the top of the battery to keep it free of dirt and debris which can also deprive the battery of voltage. Replace the battery if it is more than three years old and if you leave your boat idle for extended periods of time.
Remove the spark arrestor (on inboard marine engines and stern drives) to check that the airflow into the body of the carburetor or electronic fuel injection (EFI) throttle is adequate. Use a carburetor cleaner to spray the filtering element from the inside out to keep debris away from the engine. Spray the linkage with carburetor cleaner. Use carburetor cleaner on any varnish, oil or other buildup.
Check that the choke plate is shut when the engine is cold and open when the engine is warm. If the choke plate doesn't respond like this, check the linkage for restrictions. Examine the adjustment and check for damaged fuses or wires on an electric choke.
Check for carbon buildup in the outboard motor. Inject internal engine cleaner through the intake to remove carbon buildup from exhaust ports, combustion chambers and pistons.
Replace the spark plugs once a year. Leave as little gap as possible between the center electrode and the ground electrode without excessive tightening of the spark plugs. Check for cracked spark plug wires.
Check all hoses and drive belts of the cooling system for excessive wear or damage.
Spray water on the power head to check for excessive heat. If the water makes a popping sound on contact or turns to vapor, then the power head may be overheating.
Check for leaks in the valve cover gaskets of inboard marine engines and stern drives. Test the bolts with a socket wrench to ensure the proper tension. If the gasket continues to leak, then replace the gasket.
Rent a compression gauge to check the compression of each cylinder in your engine. Run the engine until it's warm then turn it off. Remove the spark plugs, run the engine again and check the compression of each cylinder. Check your marine engine's manual for the acceptable cylinder compression readings. Apply an ounce of engine oil into cylinders with a low compression and run the engine again. Check the compression of the cylinders again and if the reading is higher than before, this indicates damage to the rings. If the compression varies by more than 10 points between cylinders, then you may need to replace your engine.
Change the fuel filters every season.
