How to clean a spark plug

19 January 2017 Maintenance

When the boat motor, lawn mower, chainsaw, or weed whacker won’t start, the problem could be a dirty spark plug.

Here’s a quick fix to get you back on track.

How to clean a dirty spark plug

Equipment maintenance is an important part of cottage ownership. Ideally, we have the time to do a full tear-down of all the motors and make sure they are in pristine operating condition, but we all know that doesn’t always happen.

Why do spark plugs get dirty?
Spark plugs can get fouled or dirty for a number of reasons. An air-to-gas ratio that is too rich can cause the problem. This is often the result of an incorrect carburetor setting.

Damaged valve seals or piston rings can be the culprit, allowing oil to leak into the combustion chamber.

Long periods of idling or slow operation can also cause the problem, as the spark plug might not operate at a high enough temperature.

Over time, spark plugs in 2-stroke engines will often start to have some fuel, oil, or carbon build up and many people simply replace the plugs with new ones.

While plugs should be replaced on a regular maintenance schedule, sometimes you don’t have a new plug handy when you need to use the equipment.

In this case, a simple cleaning of the spark plug firing tip should fix the problem long enough to get the boat motor, lawn mower, or chainsaw started.

Remove the spark plug
spark plug socket The first step is to use a ratchet and a spark plug socket to remove the plug from the motor.

Special tip: If you don’t already have one, it is worthwhile to invest in a spark plug socket set.


What should you use to clean a spark plug?
spark plug and sand paper The quickest way to get the spark plug cleaned up enough to fire properly is to use a piece of sandpaper.

Fine sand paper grade is better than coarse. Try to use a grit level ranging from 120 to 220.

Clean the spark plug
cleaning spark plug with sandpaper Use the sandpaper to clean the dark coating off the plug by rubbing it against the centre electrode (the bump that sticks up from the centre), and the side electrode (little arm above the bump).


Make sure you clean all parts as much as possible to ensure the plug works properly.

Set the proper spark plug gap
Each spark plug has an optimum gap that should be maintained for peak performance. If you are in a pinch and simply need to get your equipment running, setting the gap isn’t critical. However, for preventative maintenance, this should be done with a spark plug gap gauge.

Reinstall the plug
Once the spark plug is clean, put it back into the motor. Only tighten the plug until it is firmly in place. Too much torque can damage the spark plug.

Other ways to clean a spark plug
Some people use a wire brush, while others take it up a notch and use a blow torch. You can also purchase a device that is specifically designed to clean spark plugs.

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Go to the Chainsaw Maintenance page.
Go to the Lawn Mower Maintenance page.
go to the Boat Motor Maintenance page.