Tired of pulling your back out trying to start your lawn mower, only to have it sputter and die? Perhaps your mower needs a new spark plug – the device that creates the electrical spark that ignites the fuel in your engine. If the spark plug is worn or bad, it can cause the mower to run rough or not start at all.
Check the spark plug annually as part of your regular lawn mower maintenance. Sometimes the spark plug can be cleaned and adjusted by resetting the spark gap at the end of the plug. If not, it will need to be replaced.
Even if you’re not mechanically inclined, you can replace a spark plug in a matter of minutes for less than $5, which makes a world of difference in helping your lawn mower start and run properly. Read on to find out how to go about it.
What You’ll Need
To change the spark plug on your lawn mower, you will need the following.
1. Spark Plug
Lots of hardware stores sell spark plugs for lawn mowers, as well as agricultural supply stores, auto parts stores, home improvement centers, and lawn mower repair shops. If you bought your lawn mower at a big box store, check there first – they often carry parts for their stock lawn mowers.
To find the correct spark plug, consult your lawn mower owner’s manual. Or, take the old spark plug with you to the store, along with the make and model of your lawn mower. Most parts stores have a reference book where you can look up the part number and compare it with your old one.
2. Spark Plug Wrench
This handy tool makes changing your spark plug a snap. Or, I should say NOT a snap, because the purpose of the tool is to help prevent the ceramic plug body from breaking! Special spark plug sockets are also available for standard socket wrench sets.
3. Spark Plug Gap Gauge
This inexpensive small gauge is used to measure the gap in the spark plug where the spark is generated. If not adjusted correctly for the plug and mower, the spark plug will not spark. Check your lawn mower manual to find the correct distance.
Step 1: Locate Spark Plug
The spark plug should be easy to find and reach. Most often they’re on the front of the mower, or possibly on the side.
Step 2: Disconnect Spark Plug Wire
Pull off the spark plug wire. You may have to wiggle it a little, but it should come right off. If it’s stuck and you have to use pliers, be very gentle and try not to damage it. Look inside the wire hood and inspect the contacts – if the spark plug wire is corroded and rusty, you may need to replace it, too.
Step 3: Remove Spark Plug
Using the spark plug wrench, loosen the old spark plug by turning it to the left (counterclockwise) and remove it.
Step 4: Check Spark Plug Gap
Most spark plugs come preset to the proper spark gap, but you should check it with a spark plug gap gauge to make sure the gap is set to the distance recommended in your lawn mower manual.
If not, tap the end of the spark plug gently on a solid surface to reduce the gap, or bend it out slightly to increase it.
Step 5: Install New Spark Plug
Install the new spark plug in the hole by hand, turning it to the right (clockwise). It should screw in easily. Don’t force the plug, since it can cause cross threading. Instead, unscrew the plug and try inserting it again.
Once the plug has been screwed in by hand, GENTLY tighten it with the wrench until snug. Don’t over tighten the spark plug, since it can cause the threads to strip or break the ceramic plug.
Step 6: Reattach Spark Plug Wire
Push the spark plug wire back onto the new plug, and that’s all there is to it. Congratulations – you’re done!
Further Information
- Lawn Mower Maintenance (article/video)
