How to Service Outboards

by Kyle McBride

Outboard motors pose no difficulty to maintain and keep in good working order. Most outboard motors use two-stroke engines, which run on a gas/oil mixture and eliminate the need for regular oil changes. Running the engine regularly is one of the best ways to keep the engine lubricated and protected from corrosion and preventing the water pump impeller from sticking to the housing and self-destructing when the engine is started. Engines that sit unused for extended periods of time, such as in areas with seasonal boating, must be serviced to restore the engine to working order. There are three basic areas that must be attended to--the carburetor, lower unit and spark plugs.


Remove the engine cowling to expose the carburetor and spark plugs. Unbolt each carburetor from the engine head with a wrench.

Remove the fuel bowl from each carburetor with a screwdriver. Remove the brass fuel jets from the carburetor body.

Spray carburetor cleaner through the jets and through the fuel passages of the carburetor body to remove any fuel varnish that may be restricting the tiny orifices that meter the fuel flow.

Reassemble the carburetors and mount them back onto the engine head. Tighten the carburetor mounting bolts firmly, but do not over-tighten them as the aluminum ears of the mounting flanges are easily broken.

Spark Plugs

Remove the spark plug wires from the plugs. Inspect the plug wires and wire boots for signs of insulation breakdown or thermal damage. Replace all of the wires if any of them are damaged.

Remove each spark plug from the engine with a ratchet and spark plug socket. Gap the new plugs according to the plug manufacturer's specifications with the plug gap tool.

Install a new, gapped plug into each plug hole and tighten them down until the crush washer that seals the plug compresses slightly. Do not over-tighten. Reinstall the wires onto the plugs.

Lower Unit

Remove the lower unit from the motor according to the motor manufacturer's procedure. Remove the water pump impeller from its housing in the lower unit.

Inspect the water pump housing for damage or scoring caused by sand or grit in the pump. Excessive scoring may lead to reduced pump output and should be repaired according to its factory recommendations.

Install the new pump impeller into the housing. Reinstall the lower unit onto the motor.

Remove the lower unit oil drain plug with a screwdriver. Observe the oil coming out and look for signs of water intrusion (milky or peanut-buttery colored oil). Replace the lower unit seals if water is detected.

Fill the lower unit with fresh oil. Refer to the owner's manual for proper oil type and amount.

Items you will need


About the Author

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