This DIY riding mower repair guide gives step-by-step instructions for replacing the spark plug on your riding lawn mower. You'll notice the engine runs rough or is hard to start if it has a broken or fouled spark plug. To keep the mower running smoothly, replace the spark plug once a year, or as often as your owner's manual specifies. Replace the spark plug with a manufacturer-approved replacement part if it's fouled or the ceramic insulator is cracked.
Use the procedure in this repair guide and video to replace the spark plug in Craftsman, Husqvarna, Murray, MTD, Toro, Troybilt and Ariens riding mowers and tractors.
Spark plug wrench
15 minutes or less
15 minutes or less
Replacing a spark plug on a riding lawn mower
This video explains how to replace the spark plug on a riding lawn mower.
Disconnect the spark plug
Park the tractor on a level surface in a well-ventilated area and set the parking brake.
Turn the ignition switch off and remove the key.
Let the engine cool.
Wear work gloves to protect your hands.
Lift the tractor hood and disconnect the spark plug wire.
Tip: Disconnect both spark plug wires if your tractor has 2 cylinders.
Disconnect the spark plug.
Remove the old spark plug
Use a spark plug wrench to remove the spark plug from the engine.
Tip: You can instead use a deep socket and ratchet to remove the spark plug.
Remove the old spark plug.
Install the new spark plug
Using a gap tool, set the gap on the spark plug to the gap specified in the owner’s manual. For this engine, the gap is .03 inches.
Thread the new spark plug into the engine and tighten it with the spark plug wrench. Tighten the spark plug firmly, but don't overtighten, so you can remove the spark plug easily the next time you replace it.
Gap the spark plug.
Reconnect the spark plug
Reconnect the spark plug wire and lower the tractor hood.
Tip: Reconnect both spark plug wires if your engine has 2 cylinders.
Warning: Undertaking repairs to appliances can be hazardous. Use the proper tools and safety equipment noted in the guide and follow all instructions. Do not proceed until you are confident that you understand all of the steps and are capable of completing the repair. Some repairs should only be performed by a qualified technician.