How To Clean a Small-Engine Spark Plug

Over time, spark plugs in small engines, like those used by lawnmowers, generators and chainsaws, can become dirty or “fouled” with carbon and oil. That can cause misfires, rough idling and other performance issues. When that happens, cleaning them can be a solution.

“Cleaning off the buildup can improve both power and fuel economy, help your small engine run more smoothly, plus extend the life of the plugs,” says Duane “Doc” Watson, technical trainer at Bosch Mobility Aftermarket.

Knowing how to clean the spark plugs on your small engines will save you the time and expense of traveling to a store to buy replacement plugs, and it could get you up and running when a new plug is not readily available.

This cleaning job is simple. It takes less than 15 minutes and saves you the $5 to $10 cost of a new plug.

Remove the spark plug

• Remove any shroud or covering over the spark plug and use your fingers to pull off the thick wire that’s pressed onto the top of the plug. If the wire doesn’t pull off, rotating it slightly from side-to-side as you pull will help.
• Loosen and remove the spark plug using a spark plug wrench.

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Examine the spark plug

• Look at the end of the plug that’s normally inside the combustion chamber of the engine.
• The tip of the spark plug will tell you how cleanly your engine is performing. Dry light gray is ideal. Black fluffy deposits indicate an engine that’s running too rich. Wet oily deposits indicate an engine that’s burning excess crankcase oil or, in the case of two-stroke engines, burning gasoline with too much oil mixed in.

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Clean the tip

• Flood the tip of the plug with rubbing alcohol and let it sit for one minute, gap-end upward.
• Scrub the entire tip of the spark plug with a soft brass or plastic brush, applying more rubbing alcohol as needed to keep the tip wet. Clean as deeply as possible in and around the tip.
• Rub the tip with a rag to further clean it, then let the plug sit in the open air to dry. If the tip is clean, dry and free of debris, proceed to the next step. Apply more alcohol and scrub again if residue remains.

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Adjust the gap

• Test the width of the gap using a spark plug gap tool.
• Increase or decrease the size of the gap as needed based on engine manufacturer recommendations. All engine manufacturers publish specifications for spark plug gap in owner’s manuals and online. Small engines typically require a spark plug gap of 0.020 to 0.030 inches.

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Re-install the spark plug

• Use your fingers to thread the spark plug back into the engine. Follow up with a wrench for final tightening.
• Push the spark plug wire down over the end of the spark plug. Rotate the rubber boot a bit one way then the other as you’re pushing it in place to make sure the connection is secure.
• Replace any shroud or covering you removed earlier.
• Test your work by starting and running the engine.

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FAQ

What should I do if my small engine won’t start?

To diagnose the problem, start with the basics, says Watson. “Check your fuel and oil levels, because sometimes it’s really that simple,” he says. “Some small engines also have a low-oil-level sensor that prevents the engine from running or starting if it is low.”

Other common causes include the battery, fouled spark plugs, clogged air filters or fuel lines, gummed up carburetor, flooded engine and cold weather (since the oil becomes thicker).

How can I prevent small engine problems from happening?

Routine maintenance is the best way to avoid small engine problems. That will also extend its lifespan. Keep the air and fuel filter clean, use the recommended fuel grade for your engine, change the oil regularly and use fuel stabilizer if your engine is not going to be used for a while.

“Since these engines are air-cooled, use compressed air to clear out debris, and wash it every now and then,” says Chris “Moose” Pyle, a JustAnswer master certified mechanic. “The high temperatures from a dirty engine will make your oil wear out and fail faster.”

About the Experts

• Duane “Doc” Watson is a technical trainer at Bosch Mobility Aftermarket. He has more than 45 years of experience in automotive repair, has trained thousands of technicians and earned many industry awards, including Chevrolet Technician of the Year and Buick Service Master of the Year.
• Chris “Moose” Pyle is a master-certified technician with 20-plus years of automotive experience, and an auto expert on JustAnswer, the expert on-demand platform.