10 Reasons Your Lawn Mower Is Sputtering(+Quick Fix)

When a lawn mower sputters, it makes spitting noises to indicate damage and an immediate need for a solution. The noise is so unusual that you cannot confuse it with other normal lawn mower decibels.

A lawn mower sputters due to clogged filters, moisture in the fuel tank, spark plug issues, carburetor issues, dirty mower deck, bad gas cap, and wrong fuel. To prevent this, clean the filters, cleanse the carburetors with cleaner sprays, remove the spark plug, and use a fuel stabilizer. 

Throughout this article, you will learn the different causes behind a sputtering lawn mower, how to fix each, and some preventive measures to keep your lawn mower long-lasting. 

Lawn mower bag

Clogged air filters

Clogged or dirty air filters are common for lawn mower owners. 

The lawn mowers will take the air from the surrounding environment through the air filters and mix it with the fuel inside the mower engine. 

When the filter is clogged with dirt and debris, the air cannot get into the carburetor and mix with the fuel. 

The dirt will also accumulate in the areas leading from the carburetor and fuel filter. 

It further troubles the fuel flow into the combustion chamber. 

How to fix it?

When your lawn mower’s air filters get dirty, you should clean them or replace them with new ones. 

If you have a foam filter, clean it with dish soap and warm water. 

After cleaning, air-dry the filter and then reinstall it inside the mower. 

If you have paper air filters, you must replace them with a new filter during maintenance. 

Check the cap of the fuel tank for excessive air. 

If you find any defect, you should change it with a new one. 

Change or clean the air filters every 3 months. 

Also read: Can You Run A Lawn Mower Without An Air Filter?

Moisture in the fuel tank

Lawn mower gas refill

High moisture content in the fuel tank or line will create several issues in the lawn mower, sputtering being a common one. 

Moisture obstructs the firing of the gasoline properly. 

As a result, it causes the lawn mower to sputter. 

The lawn mower’s engine can have water droplets due to condensation or a loose gas cap. 

Sometimes, the water droplets will be present in the fuel tank before it gets into the mower. 

Open the cap and regularly check it for water droplets inside the fuel tank. 

See whether the liquids get separated into two different phases or colors. 

How to fix it?

If you find any presence of water in the fuel tank, drain the old fuel out of the mower and pour fresh fuel into the tank. 

It will allow your lawn mower to stop sputtering and function properly like before. 

While disposing of the fuel out of the tank, you should be careful. 

Since the fuel is highly flammable, you should keep it in a safe place away from fire.

Also read: Why Is My Lawn Mower Spark Plug Wet? (3 Possible Problems+Fix)

Spark plug issues

Lawn mower spark plug

Any spark plug problems will make your lawn mower function improperly. 

This problem will make your lawn mower difficult to start. 

As a result, it will sputter and die. 

The spark plug contains 2 parts. You must examine them and find out what has gone wrong. 

The first one is the firing tip. 

Here, the metal will bend to make a gap between the metals and the electrodes. 

The metal bends will deteriorate over time, or the electrode tip will be rounded off. Such a condition will make your lawn mower sputter. 

The second one is the porcelain housing. 

This part may get cracked, causing your mower to degrade its functionality and sputter. 

How to fix it?

If the firing tip causes issues, you need to clean the tip with a wire brush. 

After that, reset the gap between the metals and electrodes by consulting the manufacturer’s manual. 

If the mower’s porcelain is the problem, replace the spark plug with a new one. 

You can do it when you regularly maintain the lawn mower for its smooth functioning. 

Try using a spark plug from a different company. 

It will let you know which works better and suits your lawn mower. 

Dirty carburetor 

Lawn mower engine repair

When you use the same lawn mower for a long time, the carburetor will become dirty, like the air filters. 

The dirt deposits will clog the carburetor over time. 

This clogging in the carburetor will make your lawn mower sputter and cause the engine to die right after the machine starts. 

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How to fix it?

Maintain a routine cleanup of the carburetor. 

There are multiple carburetor cleaning sprays available. 

Directly spray the product into the carburetor. 

The spray will loosen the dirt and clean the carburetor. 

Carburetor issues 

lawn mower fuel filter

Besides clogging, the carburetor can face several other issues which will need a professional’s attention. 

The carburetor mixed the fuel and air to increase the power and reduce the fuel consumption. 

If there is too much air, the engine’s power will degrade. 

If the air is too little, the mower will consume excessive fuel. 

When the carburetor cannot balance between the fuel and the air, the mower will sputter and die right after starting. 

How to fix it?

All mower owners are not experienced in fixing the carburetor, especially beginners. 

In that case, you should take the mower to a professional. 

The experts will inspect the problem and repair or replace the part. 

It will save you time, effort, and money. 

Also read:

Dirty mower deck 

Lawn mower blade removal

When grass in the lawn mower builds up in the mower deck, your lawn mower will sputter. 

It occurs when the grass is taller than 3 inches and wet. 

The grass will disturb the exit hole if your lawn mower contains a side discharge. 

As a result, the grass will clump instead of spreading. 

If you have a bagger, it will have a limit of holding grass. 

The extra grass will spread on your lawn if the quantity is too much. 

For mulching mowers, the buildup of grass will reduce the space above the blades to cut the grass. 

If the space is less, the cutting quality will deteriorate. 

The accumulated grass will interrupt the grass intake and exit and make your lawn mower sputter. 

How to fix it?

When your lawn mower sputters, check the underside of the lawn mower once. 

Before checking, you should remove the spark plug using a wrench for safety purposes. 

Use a scraping tool like a paint scraper to remove the excess grass from the deck. 

Afterward, use a garden hose to rinse the deck to remove the remaining dirt. Let it dry for some time.

It will help your mower to function well without sputtering. 

Also read: 8 Reasons Your Lawn Mower Is Not Bagging (+Quick Fix)

Bad gas cap

Lawn Mower Smoking

Sometimes, the lawn mower’s gas cap will be badly vented. 

Due to this, an excessive amount of air will enter the gas tank and create a vapor lock.

If this happens, the mower will act improperly and sputter. 

How to fix it?

Fixing is relatively easy. 

If the hole is obstructed, open the restricted gaps in the gas cap. 

If the gas cap has been damaged, you should replace the gas cap.

Old or wrong fuel

Gas can

Fuel in the gas stations contains around 10% of ethanol. 

Since fuel is cheaper than gasoline, many mower owners prefer fuel over gasoline. 

This fuel is sometimes ethanol-blended, which means the percentage of ethanol can be higher than 10%. 

Due to high ethanol, the moisture content in the fuel will be higher, and moisture can obstruct the ignition and make your lawn mower sputter. 

The lawn mower engine will also rust over time due to moisture. 

If you store your mower for a very long time, the fuel inside it will worsen, making it dysfunctional and sputter. 

How to fix it?

Fixing an old or wrong fuel is easy. 

You need to replace the existing fuel with new and the right one. 

You should use a fuel that contains 10% of ethanol or less than that. 

If any fuel contains higher than 10% ethanol, avoid it for your mower. 

Keep your mower from having the same fuel for a very long time. Change it. 

To renew the existing fuel, find the fuel tank and tank line. 

Disconnect the line with a pair of pliers and drain all the old fuel into a container. 

Remove the fuel bowl from the carburetor and clean it properly. 

Now, connect the fuel and the line and add the right quality fuel to the mower. 

Check for leaks too. 

Also read:

Fuel pump issues 

Lawn mower engine repair 3

The problems in the fuel pumps are difficult to diagnose. 

These pumps rely on a small diaphragm and pressure caused by the engine. 

It works when the engine turns over or runs. 

You need to check how the fuel flows through the pump. 

Remove the outflow fuel line from the pump and turn over the lawn mower engine. 

You will find an unimpeded fuel flow flowing with proper consistency. 

If the flow is slow or random, it is the main cause behind the sputtering.

How to fix it?

Avoid overfilling the tank. After refueling, stop and turn off the mower motor. 

Keep the fuel line priming tool ready if too much air enters the system. 

The tool will keep excessive air from entering the system. 

Sputtering when the blades are engaged

overgrown lawn 2

When your lawn mower sputters when the blades are still working, expect issues related to the switch, belt, and pulley. 

Safety switch 

When your mower sputters during the blades’ engagement, it could be due to a faulty safety switch. 

The safety switch is responsible for shutting off the mower when necessary. 

But, if the switch gets activated when it should not, there is a problem. Such a condition can make your mower sputter. 

To analyze the problem:

  • Find the safety switch from the underside of the mower seat. Unbolt the seat to access the switch. 
  • You might have to unscrew the locking tab and detach the mower seat from the bracket. 
  • Once you access the switch, check for physical damages. 
  • Sometimes, the switch damage is invisible. In that case, you need a multimeter to test it. 
  • If the results in the multimeter show 0 ohms, it means your safety switch is damaged, and you need to replace it. 

Take your lawn mower to a professional for the safety switch replacement.


If the mower sputters when the blades are engaged, the result is an improper belt routine. 

To fix the problem:

  • Lower the deck to the lowest setting and remove the belt guard.
  • Disconnect the rear deck pins and lift the mower belt above the pulley. 
  • Detach the front deck pins supporting the PTO cable to get access for the spring removal. 
  • Slide the deck under the lawn mower and check the belt routing. 
  • If you find a problem in the routing, check the manufacturer’s instructions about routing and rerouting the belt. 
  • If you cannot understand it, take the mower to an expert to fix it. 


The pulley in the lawn mower stays engaged by the drive belt. 

It helps in rotating the spindles. 

When the pulley gets stuck and does not spin properly, your mower will sputter during the blade’s engagement. 

To examine the problem:

  • Detect the drive belt from the mower’s pulley and engage the blades. 
  • Spin the idler pulley with your hand and check if they turn or makes a low-pitched sound. 
  • If the pulley does not turn, you need to replace it with a new one. 

Replacement is a complicated job. So, take the mower to a professional to replace the pulley. 

Preventive measures to prevent the lawn mower from sputtering 

You can troubleshoot the problems leading to the sputtering of the lawn mower yourself or with a professional’s guide. 

But the best option is to prevent sputtering to keep your lawn mower safe and encourage its smooth functioning. 

Here are some preventive tips and measures to stop the mower from sputtering:

Use a fuel stabilizer or ethanol-free gas.

A fuel stabilizer will extend the lifespan of the gasoline. 

Ethanol-free gas will burn the cleaner and help your mower to start at the first pull itself. 

Ethanol-free gas will also prevent moisture buildup in the tank and engine. 

Clean and replace the air filters regularly. 

Replace the fuel filters to smoothen the gasoline flow into the engine. 

Dirty filters will cause your lawn mower to blow smoke. 

Replace or clean the air filters every 3-4 months to prevent the machine from sputtering or smoking. 

Clean filters will prevent interruption in the airflow to the combustion chamber and several other issues. 

Check the spark plug. 

Lawn mower spark plug fix

Remove the spark plug to check the firing tip. 

If the tip is covered with carbon, clean it with a wire brush to reset the difference in the mower. 

Replace the spark whenever you see cracks or chipping off. 

When the electrode’s tip has deteriorated, replace it with the help of a professional. 

Final thoughts 

There are various reasons behind a lawn mower sputtering, like dirty filters, carburetor issues, dirty deck, bad fuel, moisture, and spark plug issues. You should find the correct one and fix it soon. 

Consult this article to find out the cause of a sputtering lawn mower. Feel free to get help from a professional. An expert can solve the problem correctly and quickly without wasting extra time and money. 

Make sure your lawn mower is always in good shape and maintained well. Regular maintenance will keep your mower from sputtering and several other issues. 

Why does my lawn mower keep turning off or running roughly?

A faulty spark plug, dirty carburetor, clogged mower deck, or moisture are common reasons behind a lawn mower shutting off. Clean the filters, refill your fuel tank, and solve the spark plug issues. 

When does your lawn mower release white smoke?

White smoke from the lawn mower indicates oil overflow or spillage. The engine will burn this extra fuel and release the white smell. However, the smoke should fade once the oil has burnt off.

Why does my lawn mower backfire?

Spark plugs, a decelerating engine, sheared flywheel key, an ill-adjusted carburetor, and the gasoline type can make your lawn mower backfire.

Reference: Lawn Mower Technology, Lawn Mower SafetyLawn MowingLawn CareMowing your lawn.


Hello everyone, My name is Richa and I am here to make you a better gardener by creating an in-depth and helpful resource for all the fellow gardeners out there. If I could help even a few people understand their plants better then I call it a success for my efforts.

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