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 riding lawn mower 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.

Instructions

1. 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.

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.

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.

 

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.