Why Do Spark Plugs Foul on a Honda Lawnmower Engine?

Overheat

• Honda engines have cooling systems, such as air cooling on the GCV 160. Engine oil also transfers heat from hot engine parts. When cooling fans or the blower hole is damaged or obstructed, the airflow into the engine is restricted and can cause overheating. If the engine becomes overheated, especially in the combustion chamber, it can damage the spark plug. Overheating on the spark plug can also happen if it is not tightened correctly. A spark plug fouled from overheating will look like a grey or white blister.

Wet Foul

• Oil leaks can foul out your Honda lawnmower’s spark plug. Oil leaks can come from worn gaskets, plugged breather valves or worn oil rings. If oil enters the combustion chamber, it interferes with the combustion process. It may not burn once the spark plugs ignite the fuel vapors. Too much oil can end up covering the spark plug during ignition and foul it out with an oily, black film covering the tip.

Cold Foul

• Honda lawnmower engines with a choke system can cause a cold foul on spark plugs. The choke can allow you to add more fuel to the carburetor, which can aid in starting a cold engine once the fuel-rich vapors ignite. Too much fuel, however, will foul the spark plug because it will continue to fire more than 1,000 times a minute without lighting anything. Excessive idling can also cause a cold foul, which is identified by a carbon coating on the spark plug.

Spark Plug Maintenance

• Maintaining the spark plug can help prevent future fouling in your Honda lawnmower engine. Install the correct spark plug as indicated in the owner’s manual and ensure the spark plug gap is within limits. Bend the electrode as needed to meet the limits. Tighten the spark plug an additional half turn once it seats the washer. Check and adjust the spark plug every 50 hours, and change it after 200 hours of service.