If your lawn mower is running rough, starting poorly, or guzzling gas, learning how to clean a spark plug on a lawn mower is a simple fix you can do yourself. This step-by-step guide for the DIY gardener will walk you through the entire process safely and effectively.
A dirty or fouled spark plug is a common culprit behind engine troubles. It’s a cheap part, but cleaning it can often restore performance instantly. With a few basic tools and about 15 minutes, you can have your mower running smoothly again.
How to Clean a Spark Plug on a Lawn Mower
This main process involves removing, inspecting, cleaning, and reinstalling the plug. Always let your mower engine cool completely before starting. Working on a hot engine is a safety risk.
Tools and Materials You’ll Need
Gather these items before you begin. Having everything ready makes the job quick and easy.
- Spark plug socket wrench (usually 13/16″ or 5/8″)
- Socket extension and ratchet
- Wire brush or spark plug cleaning brush
- Clean cloth or paper towels
- A small amount of rubbing alcohol or carburetor cleaner
- Optional: Spark plug gap tool and feeler gauge
- Optional: Compressed air can
Step 1: Locate and Disconnect the Spark Plug Wire
Find the spark plug on your mower’s engine. It’s a short, thick, porcelain-coated part with a rubber boot attached to it. Firmly grasp the rubber boot and pull it straight off the metal terminal. Do not pull on the wire itself, as this can damage the connection.
This disconnection is a critical safety step. It ensures the engine cannot accidentally start while you are working on it.
Step 2: Remove the Spark Plug
Place your spark plug socket over the plug. Attach the extension and ratchet. Turn the ratchet counter-clockwise to loosen the plug. Once it’s loose, you can often finish unscrewing it by hand.
Be gentle. You want to avoid stripping the threads in the engine’s cylinder head. If the plug is very tight, don’t force it; ensure you’re turning the correct direction.
Step 3: Inspect the Spark Plug Condition
Now, take a close look at the removed plug. Its condition tells you a lot about your engine’s health. Look at the electrode (the small metal L-shaped hook) and the insulator (the white porcelain part).
- Normal: Light tan or gray deposits on the insulator tip.
- Carbon Fouled (Dry & Black): Often caused by too much fuel, a dirty air filter, or weak ignition.
- Oil Fouled (Wet & Black): Indicates oil is leaking into the combustion chamber, which is a more serious issue.
- Worn Electrode: The metal electrode is visibly rounded or eroded. This plug needs replacement, not just cleaning.
If the plug is oil-fouled or physically damaged, cleaning is only a temporary fix. You should replace it and investigate the underlying engine problem.
Step 4: Clean the Spark Plug Thoroughly
For plugs with light to moderate dry carbon deposits, cleaning is very effective. Here’s the best method.
- First, use your wire brush to scrub away any loose, heavy carbon from the threads and the metal shell. Brush in a direction away from the insulator to avoid pushing debris into the gap.
- Next, dampen a corner of your cloth with a small amount of rubbing alcohol or carburetor cleaner. Gently wipe the insulator tip and electrode to dissolve stubborn deposits. Avoid soaking the plug.
- Use the wire brush again to carefully clean the electrode and the small metal tip it faces (the ground electrode). The goal is to reveal bare metal.
- If you have compressed air, blow off any remaining debris from the plug, especially down inside where the insulator meets the metal shell.
- Finally, wipe the entire plug with a dry cloth to ensure it’s completely clean and free of any cleaning fluid residue.
Step 5: Check and Adjust the Spark Plug Gap
The gap is the space between the center electrode and the ground electrode. This distance must be correct for a strong spark. Consult your mower’s manual for the exact gap specification (common gaps are .030″ or .025″).
Use a feeler gauge to check the gap. Slide the correct-sized blade through the gap; it should have a slight drag. If it’s too wide or too narrow, use the gap tool to bend the ground electrode very slightly to adjust it. Never bend the center electrode.
Step 6: Reinstall the Spark Plug
Carefully thread the spark plug back into the cylinder head by hand. This prevents cross-threading. Once it’s hand-tight, use the socket wrench to tighten it about a quarter to a half turn more. Do not overtighten.
A good rule is to tighten until the plug’s gasket compresses, then add a slight turn. Over-tightening can damage threads or crack the plug’s insulator.
Step 7: Reconnect the Spark Plug Wire
Push the rubber boot firmly onto the spark plug’s metal terminal until you feel or hear it click or seat completely. A good connection is essential for the spark to jump the gap you just set.
Give the wire a very gentle tug to ensure it’s on there securely. You’re now ready to test your work.
Testing Your Work and Final Tips
Start your lawn mower. It should start more easily and run with a smoother, more consistent engine sound. If the problem persists, the spark plug may be too far gone and need replacement, or there could be another issue like old fuel or a clogged air filter.
For maintenance, it’s a good practice to check and clean your spark plug at least once per mowing season. If you use your mower heavily, consider doing it twice. Keeping this small part in good shape makes a big difference in performance and fuel efficiency.
FAQ: Common Spark Plug Questions
Can I clean a spark plug without removing it?
No, you cannot clean it properly. You need to remove it to access all surfaces and the electrode gap for a thorough cleaning.
How often should I clean my lawn mower spark plug?
At minimum, once per season. If you notice performance issues, check it sooner. Many gardeners make it part of their spring tune-up routine.
What’s the difference between cleaning and replacing a spark plug?
Cleaning removes deposits to restore function. Replacement is necessary when the electrode is worn, cracked, or damaged. Plugs are inexpensive, so when in doubt, replace it.
Can I use sandpaper to clean a spark plug?
It’s not recommended. Abrasive materials like sandpaper can leave conductive residue on the insulator or remove the special metal coatings from the electrode. A wire brush is safer.
Why does my spark plug keep getting dirty so fast?
Rapid fouling often points to other problems. The most common causes are a dirty air filter, an incorrect fuel mixture (on 2-stroke engines), a clogged carburetor, or engine wear allowing oil into the cylinder.
What if the spark plug is stuck and won’t come out?
Don’t force it. Apply a small amount of penetrating oil to the base of the plug where it meets the engine. Let it soak for 15-30 minutes, then try again with steady pressure. If it still won’t budge, you may need professional help to avoid breaking the plug.