How to Replace a Riding Lawn Mower Spark Plug



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.

Repair difficulty:
Time required:

Less than 15 min.

Parts Required

  • Spark plug

For manuals, repair guides, and specific part recommendations, enter your model number.

Tools Required

  • Spark plug wrench
  • Gap tool
  • Work gloves

Before  you begin

Park the tractor on a level surface in a well-ventilated area.

Set the parking brake and let the engine cool.

Wear work gloves to protect your hands.



 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.

How to Replace a Spark Plug in a Riding Lawn Mower

Step 1: Disconnect the spark plug

Turn the ignition switch off and remove the key.

Lift the tractor hood and disconnect the spark plug wire.

 Tip: Disconnect both spark plug wires if your tractor has 2 cylinders.

Step 2: 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.

Step 3: 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.


Step 4: 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.