How to Tell if a Lawn Mower Spark Plug is Bad: 4 Easy Ways

Trying to figure out whether it’s time to replace your lawn mower spark plugs?  We have you covered.

Check out these 4 simple ways to tell if a lawn mower spark plug is bad!

lawn mower spark plug

We’ve previously covered how to balance your lawn mower blades, how to make your lawn mower faster, as well as how to remove a stuck wheel, but today we are going to be talking about spark plugs.


What Lawn Mower Spark Plugs Do

The spark plugs in your lawn mower (or anything with an engine, for that matter) are the ignition source.

It has an electrode in the middle and porcelain around it. There’s a piece of metal that arches right over the middle of the electrode.

The electrode fires and creates a spark between it and the metal tab in front of it. This spark ignites your engine and starts it.


4 Ways to Tell If a Lawn Mower Spark Plug is Bad

Troubleshooting can be difficult.

That’s why we put together this convenient guide to help you through the process.

These 4 ways should help you find out if your spark plug is bad or not.

a lawn mower spark plug tip


#1: Poor Engine Performance

Just because your engine starts doesn’t mean your spark plugs aren’t bad. A bad spark plug might start your engine but then die immediately afterward.

Maybe your mower runs for a bit but then dies in the middle of your lawn.

You’ll be able to restart your mower, but then the same thing will happen again.

As the engine gets warmer, your spark plugs are going to be less reliable if they’re faulty.

As the plugs get hotter, the metal expands further away from the electrode.

This is why the engine will fault out while running. It might also create sputtering, misfires, or popping noises while running.


#2: Hard Start

A hard start is the most common indication that your spark plugs are bad.

If your mower is being stubborn when it comes time to start, you might be able to blame your spark plugs.

This is especially true for a push mower. If you keep cranking on the rope and the engine won’t start, you’ll know where to look.

Bad spark plugs can’t make a strong enough spark to ignite the fuel and start the engine.

The more you try to unsuccessfully start your mower, the more flooded your cylinder will be – making it even harder to start.

a smaller lawn mower spark plug


#3: Physical Appearance of the Spark Plugs

If you want to be positive, you can always take out your spark plugs and take a look.

Make sure you disconnect the battery before taking off your spark plugs.

Take them out and look at the metal piece above the electrode. The electrode should be perfectly flat, so if it’s rounded then you need to replace your spark plugs.

Also, look for any chips or cracks in the porcelain area. If there’s any damage whatsoever, you need to replace them.

The final thing to physically check is the color of the plug.

a dirty lawn mower spark plug

If it’s completely black or wet, that means that you have carbon or gasoline on it. Take a wire brush to each spark plug and make them look good as new.

After that, adjust the metal tab so the gap between it and the electrode is correct. That might be all you need to fix your spark plugs (no replacement necessary).


#4: Excessive Fuel Consumption

The final indication is if you’re burning through fuel faster than ever.

You should have a pretty good idea of how regularly you refill your gas tank. If you’re filling it more often, then it’s time to check the spark plugs.

Bad spark plugs won’t allow gas to burn correctly. It either won’t fully burn or it will just burn inefficiently.

This means that your fuel consumption changes and you waste a lot more gas.

This might also present itself with a strong gasoline smell while you’re mowing.

If you smell this, stop the mower and check your spark plugs.




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