Why Does My Lawn Mower Backfire?

Why Does Lawn Mower Backfire?

As we take good care of our lawns similar taking care of lawn mowers is also important or else it can cause issues like white smoke coming out of it or backfiring. And if proper care is not taken lawn movers may also catch fire. In this article we are going to discuss backfiring lawn mowers as they are common issue that causes a lot of annoyance in the neighborhood.

Backfiring can cause a lot of damage to the lawn mower and shorten its life. You’ll be notified if your lawn mower malfunctions. I had a lawn mower with this problem a few years ago, and the loud bang caught me completely off guard. It wasn’t “I wet myself” scary, but it did make me jump. If you’re experiencing this issue, you’re probably wondering, “Why does my lawn mower backfire?” and looking for solutions. This article will explain how to fix a backfiring lawn mower.

What Causes A Lawn Mower To Backfire?

An audible bang is produced when a lawn mower backfires because gas ignites somewhere other than the combustion chamber normally. When you are trying to start your mower, while it is already running, or when you are turning it off, this can occur. Backfiring in a lawn mower is frequently caused by accelerating the engine too quickly, using the wrong fuel, using a damaged spark plug, setting the carburetor too rich or too lean, and having the flywheel key sheared.

When Does A Lawn Mower Backfire?

While using a lawn mower may backfire at various points. It could backfire while you’re trying to start it, while it’s already running, or when you turn it off. Keeping track of when your lawn mower backfires can help you narrow down what’s causing the problem, with certain factors being more likely at certain times. Below, we’ll go over each of the three scenarios and outline the most likely cause in each, as well as potential solutions for you to try.

Why Does The Lawn Mower Backfires And Then Die?

If you’ve been attempting to start your mower but have been unable to do so, and all you see is your lawn mower sputtering and backfiring before dying, this often indicates that the engine timing is incorrect. If it’s backfiring through the carb, I’d recommend inspecting the flywheel. When it comes to mower engine timing problems, the most common cause is a damaged flywheel.

How are lawn mower flywheels damaged? Well, it could simply be wear and tear over time, but the most common reason why flywheel breaks is you ran your mower over a rock and hit it. If there is a severe collision, the flywheel key may be sheared.. If there is a severe collision, the flywheel key may be sheared.

Also read: Why Lawn Mower Won’t Start When Hot And How To Fix It?

Causes Of Lawnmower Backfiring Issue

The primary cause of a lawn mower backfire is a lean fuel mix. As a result, there is a lot of air in the fuel mix, which causes incomplete combustion. When this mixture enters the exhaust system, the leftover fuel spontaneously combusts, causing your engine to backfire.

So, what causes a fuel mix to become overly lean? One of the most common errors is decelerating your engine too quickly. The engine’s timing becomes out of sync with the throttle as it closes quickly. This degrades the fuel mix and eventually causes a backfire.

The final likely cause of your engine backfiring is improper engine tuning. It’s possible that your timing is too advanced or that your fuel mix is a little leaner than usual. This could have unintended consequences when specific operators who are unfamiliar with the machine’s new settings operate it.


The most likely cause of the bang is your lawn mower backfiring. It can be a nuisance to both the operator and those nearby, necessitating an effective solution to the problem.

As you slow down, gradually lower the engine’s speed– The combustibility of fuel increases with the amount of ethanol in it. As a result, while operating the lawn mower, you might experience premature explosions outside of the engine chamber, which would cause the engine to backfire.

It is necessary to upgrade cooling systems -The combustion process won’t utilize the mixture within the chamber effectively if your engine is operating at temperatures above normal.

The engine’s timing must be checked to ensure proper ignition – Incorrect timing will also result in inefficient fuel consumption. This can have a negative impact on the fuel mix within the engine, causing it to backfire.

Failure of the valve system can also result in improper fuel intake and exhaust flow, which can cause the engine to backfire. We wrote a detailed article about When to Change Spark Plug on Lawn Mower, which you can read to determine whether or not you should change your spark plug.

How To Avoid Lawn Mower Backfiring?

How To Avoid Lawn Mower Backfiring?

Preventing engine backfires does not require any specialized care or skill. All you need to do is a few simple steps to take care of your lawn mower. Maintain and service your lawn mower regularly. Replace engine internal components regularly and use high-quality fuel. These will not only make your engine run more smoothly, but they will also ensure that the fuel mix is rich enough for optimal combustion.

One more way to avoid a backfiring engine is to not run it when the temperature outside is high. This may cause more volatile fuels to evaporate more quickly, while also raising engine temperature. The combination of the factors mentioned can result in an incomplete combustion process while the machine is running, resulting in a backfire.


A lawn mower that backfires can catch you off guard, and your first instinct is to suspect that something is seriously wrong. However, many times, all that is required is a minor adjustment to either the mower’s hardware or the way you use your mower. I hope this guide helps you get back to backfire-free mowing as soon as possible. Best wishes!

Frequently Asked Questions

A lawnmower backfire produces an unexpectedly loud noise, catching you off guard as you finish up your yard work and turn off the lawnmower. When fuel ignites outside the engine, usually in the muffler, this causes a backfire. The backfire will not harm your engine, but it is frequently a sign of a mechanical issue.

A backfire occurs when unburned fuel in the exhaust system ignites, even if there is no flame in the exhaust pipe itself. When a car backfires, you may see a flame, but most of the time, you will only hear a loud popping noise followed by a loss of power and forward motion.

Popping sounds from lawn mower engines can startle. Your lawn mower is backfiring when you hear that noise, just as a car engine can backfire when you hear a similar popping sound. To keep your machine operating when you hear that noise, it’s imperative to locate the issue’s root cause as quickly as you can.

Too Often, the intake manifold has unwanted wake-up results because too much fuel is persuaded from it, which could harm the intake motor. A portion of the exploding mixture also passes through the carburetor. knowing the location of carburetor will help solve the problem of improper carburetor adjustments or a vacuum system leak.

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