A spark plug is a small cylindrical device fitted on the engine to deliver an electrical spark that ignites the gasoline/air mixture in the combustion chamber, enabling the engine to run. A bad lawn mower spark plug won’t perform its function as needed.
Several things can make a lawn mower spark plug go bad. They include wear and tear, moisture, overheating, electrode damage, carbon buildup, and oil deposits on the spark plug. A lawn mower not starting is a major sign of a faulty spark plug.
What do bad spark plugs look like?
To know the state of your mower’s spark plug, start by disconnecting the spark plug wire from the engine. Use a wrench and a recommended spark plug socket to remove the spark plug from the engine.
Carefully examine both ends of the spark plug and the socket where it sits. If the spark plug is bad, it will appear as follows:
- Black with a chunk of carbon buildup in the gap between the sparking end and the hook-shaped piece of metal on the spark plug end.
- Simply dark with carbon residue built up on the ends but not spanning the gap
- Gas or oil residue on the spark plugs and/or where they sit
- Physically damaged on end with the overhanging piece of metal.
Sometimes it can be impossible to tell if a spark plug is bad or damaged by just using your eyes. The component can fail internally, causing its electrical system to stop working. In this case, you may need a technical assessment.
Depending on the issue’s magnitude, you may simply need to clean the spark plug and resume normal operations or replace it.
How to Change Lawn Mower Spark Plug
Changing a lawn mower spark plug is a simple DIY task involving locating it, removing it, and replacing it with a new one designed for your lawn mower model. Here are the steps for changing a lawn mower spark plug.
- Purchase the right type of spark plug for your lawn mower as the user manual directs. Spark plugs are not universal.
- Position your lawn mower on flat ground and ensure you can locate where the spark plug is on the engine. Sometimes it may be covered in the mower housing.
- Disconnect the spark plug cable to prevent the engine from accidentally starting
- Fit the spark plug socket over it and turn counterclockwise to remove it. If it’s too tight, apply a WD-40 or any lubricant and wait for it to soften for easier removal.
- Install the new spark plug and gently tighten it using a spark plug socket and wrench where necessary. Be careful not to overtighten it as this can damage it.
- Reconnect the spark plug wire and start the lawn mower engine for testing.
Pro Tip: Spark plugs should be changed during a lawn mower tune-up every season. This should be in spring as you prepare to start mowing. Spark plug inspection should be done after every 25 hours of use or more often when mowing in harsh conditions.
How to clean lawn mower spark plug
Sometimes after inspection, you may realize that your mower’s spark plug can be cleaned and used again. Carbon buildup or oil deposits can be removed by cleaning. You’ll start by removing the spark plug from the lawn mower.
Then use a recommended spray-on cleaner and a wire brush to remove any buildup. Before reinstalling it, ensure the component is in good condition without burned electrodes or cracked ceramic.
Using the spark plug gauge, measure the gap between the curved and straight electrodes. A few adjustments may be needed to correct any increase in the size of the space. This is done by gently bending the curved electrode inwards using a gauge.
Bad lawn mower spark plugs can give a bad mowing experience. Always clean or replace your mower’s spark plug before mowing in spring. Additionally, be sure that your lawn mower has fresh fuel, the blades are sharp, and the air filters are clean.