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8 Reasons Why Your Lawn Mower Sputtering (Tips to Fix)

8 Reasons Why Your Lawn Mower Sputtering (Tips to Fix)

Is your lawnmower sputtering? If yes, you’re at the right place! There can be plenty of reasons why a machine doesn’t function properly. The same goes for a mower!

In this post, we’ll go through all the possible causes why your lawnmower might be sputtering. And, don’t you worry; we’ll be sharing how you can solve the issues as well! Let’s get started, shall we?

1. Moisture in the Fuel Tank or Fuel Line

Moisture in the Fuel Tank or Fuel Line

Any moisture content in the fuel tank or the fuel line can cause problems in the engine. It will obstruct the ignition of the gasoline properly, thus, causing your lawnmower to sputter.

Your mower’s engine tank may contain water droplets from the condensation, or a loose gas cap or water droplets may be present in the fuel container before it even gets to the mower.

So, you need to regularly open the cap and check for the presence of water inside the tank. You can check for the presence of water by seeing whether the liquids are separating in two different phases or are of two different colors.

How to fix it?

If there’s a presence of water inside your tank, you can simply drain the old fuel out and pour a fresh lot of gasoline for the proper functioning of your lawnmower.

You should also be careful enough to safely dispose of the fuel that you have removed from the tank of the mower as it is highly flammable.

2. Clogged or Dirty Air Filters

It is one of the most common problems that cause lawnmowers to sputter. The mowers take the air from the surrounding through air filters and mix it with fuel inside the engine. So, if the air filter is clogged or dirty, it will affect the flow of air into the carburetor.

The dirt can also be accumulated in the parts that lead from the carburetor and the fuel filter that may cause the disturbance in fuel flow towards the combustion chamber.

How to fix it?

You have two options for fixing clogged air filters. You can either clean the air filters, or you can replace them with new ones. If you have a foam filter, you can clean it with a drop of dish soap and warm water. Remember to air-dry them before using them again.

But if you have paper air filters, you must replace them during the maintenance of your mower. You need to check the cap of the tank for too much air, and if any defect is seen, you should immediately replace it with a new one.

3. Spark plug issues

Any spark plug issues can make your lawnmower function poorly, make your engine difficult to start, run poorly, and eventually die. There are two parts in the spark plug you need to examine to find out the problems.

The first one is a firing tip where a metal bends and creates a gap between metals and electrodes. Here the metal bends might have deteriorated, or electrode tips may be rounded off, thus, causing the mower to sputter.

The other one is the porcelain housing which might be cracked, causing the lawnmower to degrade in its function.

How to fix it?

If the firing tip of your spark plug is causing problems, you can clean the tip with the help of a wire brush and reset the gap between metals and electrodes following the manufacturer’s specification.

However, if you are having problems with porcelain housing, you need to replace the spark plug with a new one. You can also replace your spark plug during every maintenance session for the smooth functioning of your mower.

Moreover, try using a spark plug from a different company to find out if it works better than the original one.

4. A Dirty Mower Deck

A Dirty Mower Deck

If the grass of your lawn builds up in the mower deck, it may be one of the reasons why your lawnmower is sputtering. It usually happens when you have tall and wet grass on your lawn.

If you have a side discharge mower, the caked grass disturbs the exit hole, and the grass clumps instead of spreading evenly. If you have a bagger, it will have its limit of holding a certain quantity of grass, and if the quantity exceeds, then the extra grass will be spread on your lawn.

And finally, for the mulching mower, the caked grass decreases the space above the blades for the grass to be cut.

So, if space is reduced, then there will be degradation in the quality of the cut. This caked or built grass disturbs the intake and exit of grass, thus rendering your lawnmower vulnerable to sputtering.

How to fix it?

If you face such a problem, consider checking the underside of your lawnmower. However, before inspecting the mower, you must remove the spark plug with the help of a wrench for safety purposes.

Once you’re done, you can simply use a scraping tool such as a paint scraper to remove the excess grass from the mower deck, thus helping the lawnmower function smoothly.

5. Old Fuel or the Wrong Fuel

Old Fuel or the Wrong Fuel

Fuel obtained from gas stations generally contains around 10% ethanol. As this fuel is cheaper than pure gasoline, many mower owners are drawn towards the fuel.

However, this ethanol-blended fuel is known to burn fast and, as a result, melt plastic parts. It might be the reason why your lawnmower is sputtering. On the other hand, if you’ve stored your mower for too long, the fuel in it might have gone bad, leading to a dysfunctional mower.

How to fix it?

Fixing the old or wrong fuel issue is relatively easy. All you have to do is replace the existing fuel with new fuel, and we recommend you to use fuel with as little ethanol percentage as possible, not more than 10%.  

To renew the fuel, firstly, you have to locate the fuel tank and fuel line tank. Then, disconnect the fuel line using a pair of pliers and drain all your old fuel into a container. Remove the fuel bowl from the carburetor and clean it.

Connect the fuel bowl and fuel line, and finish off by adding proper quality mower fuel to the mower. Remember to check for any leaks.

6. Filthy and Clogged Carburetor

If you’ve been using the same mower for a while, the carburetor might have become filthy, and the gunky deposits might have clogged it. Such clogs might result in lawnmower sputtering and also cause the engine to die after starting.

How to fix it?

To fix this problem and prevent it from happening again, all you have to do is clean the carburetor routinely.

There are various carburetor cleaners available that you can directly spray into the carburetor intake. Doing so will loosen up the gunks, ensuring that they won’t clog the carburetor.

7. Carburetor Issues

Carburetor Issues

If your mower carburetor is dirty, you can simply clean the gunk using cleaners. But there might be other complex carburetor issues that might even require professional help.

The carburetor combines fuel and air in such a way that it maximizes power while minimizing fuel consumption. If there’s too much air in the combination, the engine’s power degrades. And on the other hand, if there’s not enough air, the mower will consume too much fuel.

So, when the carburetor cannot balance between the two, your mower might sputter and eventually die.

How to fix it?

If you’re not experienced in fixing carburetor issues or, let’s say, you’re such a beginner in DIY lawnmower repair; we’d recommend you not to try fixing carburetor on your own.

We’d recommend you consider taking help from experts. They’ll know exactly what to repair and what to replace, which will save you a lot of headaches, time, and effort.

8. A Bad Gas Cap

Sometimes, the mower’s gas cap might be improperly vented. As a result, the amount of air getting inside the gas tank is so much that it causes a vapor lock. If that’s the case, it might be the reason why your mower has been acting crazy.

How to fix it?

Fixing this issue is quite easy. If you notice that the hole is restricted or the gas cap is damaged, you can simply replace the gas cap.


Finding out what might be the reason that your lawnmower sputtering can be tricky. However, we believe that this post has given you quite a bit of insight on how to check for the causes one by one.

The fixing part can be challenging as well, at least for some of the problems. So, if you’re not sure what you’re doing, we’d definitely advise you to seek expert’s help rather than trying to figure it out on your own, which might do more harm to the mower than good.

Let us know once you figure out the reason why your mower was sputtering! And, if you have more queries, you know where to leave the comment!

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