How to Get your Lawn Mower Running - Spark Plugs and Ignition System

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By fishermon
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If you lawn mower does not start after you have made sure it is properly cleaned and free from debris (see my article "How to Get your Lawn Mower Started - Cleaning the Mower"), the next thing to do check is the fluids, (see my article "How to Get your Lawn Mower Started - Check Fluids"), the next thing to do check is the air filter, (see my article "How to Get your Lawn Mower Started - Check the Air Filter"). If you still can't get your mower started check the spark plugs and ignition system. When a lawn mower won’t start it’s usually either because of “no fuel or no spark”. So let’s look at the spark.

Difficulty: Moderate

Instructions

Things You'll Need:

Socket Set
Wire Brush
Test Light
Screw Driver set
Electrical Tape

Step 1

Kill Switch

Make sure the safety switch (or kill switch) is working properly. This is the lever you pull back before starting the mower. Verify that the cable is engaging the switch and verify that the mount (or bracket) that stabilizes the cable to the lawn mower handle is attached properly. A broken bracket will cause malfunction (see picture).
Step 2

Removing Plug

If switch is working properly remove spark plug and check for spark with a tester. If you do not have a tester you can remove plug then re-attach plug wire then ground the base of the plug to the engine block. Have someone pull the pulley cord for you while doing this. Make sure not to touch any part of the plug while doing this or you will get a very unpleasant jolt. You can even tape the base of the plug to the block or use some other method to avoid touching it at all.
Step 3

When checking for spark try it in a garage or dim area so you can see better. If there is little or no spark, clean the spark plug with a wire brush and retry.
Step 4

If still no spark: replace as necessary using a spark plug wrench. usually a 13/16” or 5/8” deep wall socket.
Step 5

After you’ve replaced the spark plug and you still get no spark; check the spark plug wire for cracks or damage that could cause an arc before it reaches the spark plug. You can usually fix this problem with a roll of electrical tape. You should pay special attention to the boot that connects to the plug. These connectors are usually weak and damage easily. Sometimes when removing the plug wire from the plug you can damage the connector in the boot. The simple solution for this would be to remove the boot and pinch the connector back into the wire and then slide the boot back on.
Step 6

If none of the above works, check the coil using a test light. Touch the tester, which is grounded to the engine frame to the coil terminal while someone pulls the cord. If it lights up the coil should be ok so you will probably have to replace the spark plug wire. Depending on the model lawn mower, you may be able to replace just the wire, but typically the wire and the coil are sold as one unit.
Step 7

I hope this information has been helpful. Now go mow that lawn!!

If your lawn mower still does not start after cleaning the mower, go my article titled "How to Get your Lawn Mower Started - Fuel System".

GOD BLESS,

Jesse

Comments

Alisiane said

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on 10/20/2008 This is one of those topics that I never even bothered to consider in thinking about buying a house - apartment living makes all of this someone else's responsibility, and in my mind's eye, when I DO need a lawn mower it will run smoothly and effortlessly from purchase until I buy a new one...thanks for the reality check. :-)