Why do Lawn Mowers Backfire?

Why do Lawn Mowers Backfire?

Lawn mowers are a great way to keep your yard looking nice and tidy. However, they can have their downsides too. One of the most common problems you might come across is that the lawn mower starts backfiring when it’s running.

Sound like a problem you’ve been experiencing? Here, are some things to consider and do if your lawn mower starts backfiring.

What could be the problem?

If your lawn mower is frequently starting backfiring, there could be some problems that are stopping it from running properly. Many of these problems can be related to the mower’s power source, which is often the gas tank.

By changing to a different fuel or getting an electric mower, you can improve your mower’s fuel consumption and increase its battery life. Is there an engine problem? If your mower is constantly backfiring, you may have an engine problem.

A faulty engine can affect the mower’s power supply, which can be a result of damage to the battery. There are some things you can do to diagnose the problem and repair it. Go to your mower’s owner’s manual.

Most mowers have an owner’s manual that contains instructions about how to start, repair, and maintain the mower.

Rule out the obvious

Before you start dealing with your mower, you need to determine if it is something that is really wrong with it or if it’s just a matter of a bad trigger. First of all, is the lawn mower jammed? If so, chances are you need to start the engine and get it working. Or maybe the battery’s dead.

To check the actual battery, turn off the mower and leave it off for a moment. Wait for the engine to catch on fire or something. If you have determined that the lawn mower is not faulty in any way, you can check what’s really wrong.

In the presence of bad triggers, such as weak batteries, the lawn mower will usually backfire when the engine starts. What is it about your lawn mower that is triggering the backfire?

Checking the air filter

One of the things that people often forget to check is the air filter. The air filter is the small circular piece that’s fitted over the lawn mower’s gas tank. So if the air filter has become dirty, your lawn mower could start backfiring when you start it up.

If you have the lawn mower serviced regularly, then you probably have a clean air filter. However, if your lawn mower doesn’t have a fixed air filter, you can fit one yourself. Here’s how: Cut a small piece of adhesive tape (this is what you should do anyway when cleaning your mower) to fit over the top of the air filter so that the cotton takes it shape. Ensure that the tape is secure on the filter and that it doesn’t slip out.

Disconnecting the spark plug wire

If your mower seems to have a bad tendency to backfire when you start it, the first thing to do is disconnect the spark plug wire, as the wire typically gets caught on things like a rake, and can lead to the mower backfiring.

While your mower has you unplugging the spark plug wire, you might want to check the settings on the machine. With an electric lawn mower, you have the ability to adjust its speed and how much gas is required.

You can do this with the ignition key – when the key is turned on, the engine will ignite and you can adjust the speed accordingly.  While working on your lawn mower, you should pay attention to the various parts and attachments you’ve attached to it, to ensure they’re still intact.

Cleaning the carburetor

If you feel like your lawn mower isn’t starting because the grass-cutting blade is blocked or clogged, check to see if your lawn mower is dirty and has a buildup of excess oil or grime on it. These pieces of dirt can get into the blades of the lawn mower, stopping them from running smoothly.

Cleaning them with a damp sponge or a clean cloth can do the trick, as can hosing them down with a hose. Fuel Another possible reason why your lawn mower doesn’t run correctly is because it’s not getting the fuel it needs.

When the grass-cutting blade is clogged, it can break down and get stuck in the engine. To make sure that your lawn mower is getting enough fuel, pump it and clean out the carburetor. Then, run your mower a few minutes before you plan to use it to give it a full tank of fuel.

Cleaning and lubricating the mower drive belt

One of the most common causes of backfire is a build up of dirt or other gunk under the drive belt. Make sure you give your mower a thorough clean. You’ll need a wire brush to remove the grime. To clean your belt, put the brush on top of the drive belt and use circular motions to remove the dirt.

Rinse the brush in hot water and apply a little oil. If the belt doesn’t move freely, you might have a low-friction spot or grinding rust in it. If that’s the case, it’s time to take your mower to the garage for a check-up.

Not every mower will backfire. When one does, it’s often due to a lack of lubrication under the engine. Make sure your machine has the proper amount of lubrication.

Start-up Problems

In the beginning, you might have thought you were starting the lawn mower, but that was actually it trying to start backfiring. This is most often caused by the engine running too hot when it’s cold out. There’s no real way to test for this, other than restarting it and checking to make sure the engine is cold.

Your lawn mower may be ramping up quickly when you push it. This can cause the engine to backfire. If you see an intense backfire that’s almost immediate, unplug the lawn mower and let it cool off for a few minutes. If it doesn’t cool off, leave the mower unattended and the backfire should stop. Bad Wheel Ergonomics Lawn mowers do not roll easily on their own.

Excess Gasoline in Tank or Carburetor

Gasoline on a lawn mower gets trapped in the carburetor, leading to backfire. And there are two ways you can correct this. Locate the Fuel Line and Pumping Mechanism It’s easy to miss where the fuel line and tank are, but if you can spot them, you can check it for leaks.

If you can’t see them, you can always get a professional to take a look. If your tank has been leaking, remove it and inspect the fuel line. Once you’ve found the culprit, you should be able to find the hole in your carburetor or a leaky fuel line by looking at your lawn mower’s exhaust system.

There should be a little hole or a small “block” where the fuel should exit. If you can see the hole in your carburetor, this is a sign that your mower has been leaking gas and need new parts.

Malfunctioning Spark Plug

This is usually a problem with the spark plug. If it is cracked or damaged, it is more likely to get stuck on the spark plug ring or get damaged in the firing of the engine. Broken Fuel Injectors This could be caused by the high levels of engine fumes when you’re mowing, or if you’ve not refilled your fuel tank recently.

Sometimes your engine oil may become too thin, this is a common problem with older lawn mowers. You may notice that when you start the mower, it doesn’t start up properly. A thin engine oil also means that it could lose efficiency quickly, so make sure you get it topped up often.

Switched Oil Filters If you don’t change your engine oil often enough, you may get a gas or oil filter that gets switched incorrectly.


Backfiring is a common problem, but it’s one that lawn mowers are well designed to solve. The fix, if the issue is actually with your mower, should be simple, and you should have no problem getting it working again. We hope you never experience backfiring again, but if it does, keep calm, relax, and keep trying!

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