How To Fix Lawn Mower Sputtering: Common Reasons & Easy Fixes!

Sputtering is a common lawn mower problem that can ruin your lawn maintenance experience.

The lawn mower is a must-have lawn care tool. Using a lawn mower saves time and keeps your grass looking cleaner, greener and serener. It is because a lawn mower cuts the grass far better than manual trimming, which adds to the lawn’s beauty and keeps your grass from rusting and falling victim to diseases. Like other machines, a lawn mower also needs proper maintenance. I mean, who wants to change his lawn mower every year or so, do you?

How To Fix Lawn Mower Sputtering: Common Reasons & Easy Fixes

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Proper lawn mower maintenance includes changing engine oil, sharpening the mower’s blades, cleaning the carburetor and many other things. However, sometimes despite all your efforts, your mower can start causing problems. And one of the most common problems that nearly every lawn owner comes across is lawn mower sputtering. 

The most common reasons behind lawn mower sputtering are low-quality fuel, clogged carburetor, clogged air and fuel filter, faulty spark plug, too much moisture in the fuel tank and the use of a bad gas cap. Find the underlying issue, and you have already fixed half of your lawn mower sputtering problem.

Keep reading this article to learn more!

What Does It Mean When A Lawn Mower Sputters?

What Does It Mean When A Lawn Mower Sputters?

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Lawn mower sputtering usually indicates a filter, spark, and air/fuel injector problem.

Lawn mowers work when a mixture of air and gas enters the combustion chamber, where a spark plug ignites it. The ignited, hot and expanding gas pushes the piston, which rotates the crankshaft to which mower blades are attached.

Lawn mower sputtering means that the engine is not achieving total combustion. It is usually a sign of a clogged filter or a malfunctioning spark plug and air/fuel injector. Usually, you can tell right away that your lawn mower is sputtering. It backfires, sounds odd or feels like the mower’s engine is not working correctly.

However, the problem can sometimes be more severe and needs professional attention. Nonetheless, below are a few common reasons why your lawn mower might be sputtering, along with some easy fixes.

Why Does My Lawn Mower Sputter And Stop?

Moisture In Fuel Tank/Line

Moisture In Fuel Tank/Line

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Moisture causes problems with ignition, causing your machine to sputter.

One of the most common reasons why lawn mowers sputter is the presence of moisture in fuel tanks or fuel lines. This obstructs the ignition, which may result in lawn mower sputtering. So, you need to regularly check your mower’s fuel tank for the presence of water. So, if you see liquid separating in two different phases in your fuel tank, it means there is moisture.

You can simply drain this fuel and pour fresh fuel into your gas tank to get your lawn mower working normally. Also, make sure that you dispose of the old fuel with care as it is still highly flammable.

Old Fuel/Wrong Fuel

Old Fuel/Wrong Fuel

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Using ethanol-rich fuel is also one of the main reasons for lawn mower sputtering.

The gas that you buy at pumps contains around ten percent ethanol. This works fine for cars, but experts suggest you do not use it in your lawn mower. Ethanol-containing fuel is known to burn fast, which can melt parts of your mower’s engine. Melted mower parts might result in the lawn mower sputtering.

Moreover, the fuel goes bad when stored for too long, which might also cause your lawn mower to malfunction. All you have to do to fix this issue is use a fuel with a lower ethanol concentration. Moreover, if your lawnmower has been sitting idle for too long, replace all the fuel before using it again.

Dirty/Clogged Air Filters

Dirty/Clogged Air Filters

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Clogged air filters obstruct normal airflow causing the lawn mower to sputter.

Clogged air filters are another common reason behind lawn mower sputtering. Lawn mowers need a proper mix of air and fuel to function correctly. However, when the dust filter gets clogged due to extensive use, it blocks sufficient air from reaching the combustion chamber, resulting in lawn mower sputtering.

To fix this issue, you have two options. Either you can replace your old filters with new ones, or you can properly clean your lawn mower’s air filters. To clean the filters, you can simply wash them with soap water. However, make sure that you do not damage the filter and use them after air-drying.

A Bad Gas Cap

A Bad Gas Cap

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A lousy gas cap can cause a vapor lock, resulting in a malfunctioned mower.

Another reason why lawn mower sputtering occurs is an improperly vented gas cap. The gas cap is responsible for letting an adequate amount of water into the fuel tank to occupy the space during fuel consumption. However, if the cap lets in too much or too little air, it can result in a vapor lock. However, do not worry!

Fixing lawn mower sputtering due to a faulty gas cap is pretty straightforward. Look for any restricted gaps in the gas cap and open them. And, if the gas cap has been damaged, simply replace it with a new one.

Dirty/Clogged Carburetor

Dirty/Clogged Carburetor

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Gunky deposits can form over time inside the carburetor, limiting its function.

When you use your lawn mower for a long time, it starts getting filthy, and over time, gunky deposits start to form inside it. These are a by-product of combustion, and there is no stopping it. Such deposits can cause the engine to die after starting or reduce the efficiency of the carburetor, resulting in sputtering.

The best way of solving this issue is to clean the carburetor of your lawn mower routinely. Doing this will soften the gunky deposits and prevent carburetor clogging. A carburetor cleaner spray is the best way to do this job.

RELATED: How To Locate and Clean The Carburetor On A Lawn Mower? | A Beginners Guide

A Dirty Mower Deck

A Dirty Mower Deck

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A dirty mower deck is a common issue for lawn mower sputtering in lawn tractors. 

Another common reason why your lawn mower is sputtering is a dirty lawn mower deck. The problem is noticeable when mowing a lawn with wet and tall grass. The space inside the mower deck reduces when the grass starts clumping and caking there. This obstructs the gas ventilation, which might make your mower prone to sputtering.

All you have to do to fix this issue is to clean your mower’s deck. You can use a scraping tool to remove grass from the deck, and the mower will start running smoothly again. 

Spark Plug Issues

Spark Plug Issues

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A faulty spark plug results in the engine running poorly and shutting off.

Damaged or worn-out spark plugs can make your lawn mower function poorly by making your engine difficult to start, run poorly and die. Upon examining that plug, if its tip is dirty, simply clean it with a brush.

However, sometimes the plug might be damaged and will need to be replaced. Experts usually suggest replacing the mower’s spark plug every year to avoid running into such issues, which can be pretty frustrating.

Carburetor Issues

Carburetor Issues

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A carburetor mixing duel and air in an incorrect ratio can also result in lawn mower sputtering.

In addition to a dirty carburetor, there are numerous other problems that can cause the lawn mower to sputter. For instance, when the mower is not mixing the fuel and air in a correct ratio, it can either cause the lawn mower to sputter or consume too much fuel.

This is a problem that needs professional help, and you will have to consult an expert as he will know exactly what to repair and what to replace.

Conclusion | Lawn Mower Sputtering

Fixing lawn mower sputtering is not difficult if you know what to look for, and in this article, we have introduced you to the most common reasons for lawn mower sputtering. However, if you are still unsure, we highly recommend you seek expert help and not try fixing your lawn mower on your own.

Finally, make sure that you keep your lawn mower in good shape and properly maintained. This will help you avoid not only sputtering but also numerous other lawn mower issues as well. 

Frequently Asked Questions (FAQs)

What causes a lawn mower to backfire?

Common reasons that could result in a lawn mower backfiring are a compromised spark plug, decelerating the engine too quickly, a sheared flywheel key, the way the carburetor is set up and the type of gasoline that you’re using.

Why is my lawn mower smoking and sputtering?

The reason lawn mowers sputter and smoke is that the engine is not getting enough air or receiving a too-rich fuel mixture. As a result, fuel does not get adequately burnt, creating smoke and sputter.

Why does my lawn mower keep shutting off?

A faulty spark plug is the most common reason behind a lawn mower that starts and then dies. However, it could also be due to a dirty carburetor, clogged mower deck or moisture in fuel tanks and fuel lines.

What does white smoke coming out of a lawn mower mean?

If you see white smoke coming out of your lawn mower, it means that there is an oil spillage, and the engine is burning oil instead of fuel. It is usually not a serious issue; you can fix it by letting the engine idle until the smoke clears.

Why is my lawn mower running rough?

The lawn mower runs rough when there is moisture in the fuel tank, the air filter is clogged, the spark plug is faulty, the gas cap is ventilating abnormally, the ground speed is too fast, or the choke is in the wrong manner.

Sources for Further Reading

Lawn mower tune-up – UDAILY, University of Delaware

Lawn mower safety tips – University of Iowa Stead Family Children’s Hospital

Safety Tips for Lawn Mowing – University of Utah Health Hospitals and Clinics

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Morgan Daniels

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