House Grail is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Why is My Lawn Mower Sputtering? 8 Possible Reasons

cropped black and blue lawn mower on grass

Lawnmowers are notoriously complicated for performing such a simple job. There is a lot that can go wrong with a lawnmower, including sputtering. If your lawnmower is sputtering, there are many potential reasons why. Each reason has its own fix that you can typically do yourself.

However, figuring out exactly which reason is to blame can be challenging. Often, you simply have to go about trying to fix the easiest potential problems first and slowly work up to more difficult problems. We’ll take a look at all of the potential options below.tool divider

The 8 Reasons Why Your Lawn Mower Is Sputtering

1. Moisture Build-Up in Fuel Line

Moisture build-up is a significant problem for lawnmowers, but it is a common problem. Your lawnmower lives outside, so it commonly comes into contact with moisture. If moisture builds up in the fuel tank, then your lawnmower will have a harder time starting. Usually, this is caused by a loose gas cap, which leads to condensation finding its way inside the fuel container.

You’ll be able to check for water by looking at the gas tank. If you see one liquid on top and a different color liquid on the bottom, then you need to drain the tank and refill it.

lawn mower on grass
Image By: Skitterphoto, Pexels

2. Clogged Air Filters

Your lawnmower has to intake air to work properly. If the air filter is clogged, it will be unable to take in the amount of air it needs, which can lead to sputtering. The easiest way to check for this is to take a look at your air filters. We recommend cleaning them if they are at all dirty. If you clean them and your mower still doesn’t work, there is likely a different problem involved.

How you clean them will depend on your lawnmower. For this reason, you may want to pull out your manual for instructions on how to access the air filters and clean them properly. Usually, you simply use dish soap and warm water to remove the dirt and grime from the lawnmower.

Sometimes, you’ll need to completely change your air filter instead of cleaning it, and you should have a few extra filters on hand to change them as necessary.

3. Dirty Deck

If you have tall and wet grass in your yard, it can build up in the mower deck and cake any openings. This will eventually bog your mower down and cause problems. Sometimes the caked grass will also prevent your mower from cutting grass by stopping the blades.

Luckily, this problem simply involves cleaning the mower deck. While this can take a few minutes, it is not nearly as complicated as some of the other options on this list. Paint scrapers work well for removing this excess grass.

red lawn mower in the field
Image Credit: Piqsels

4. Incorrect Fuel

If your fuel is not the right mix for your mower or is old, then it may not provide the right amount of power to start your mower. This problem often occurs when mower owners utilize fuel instead of gasoline. You should always use the fuel directed in your mower’s manual. Otherwise, you can cause minor problems like sputtering or permanently damage your mower.

Luckily, if you just added the incorrect fuel or simply have old fuel, all you have to do is replace it with the new, correct fuel.

5. Spark Plug Problems

Your spark plug has a limited lifespan and you will have to change it eventually. If your lawnmower has an older spark plug, it may stop starting altogether. Usually, you can examine your spark plugs to find out if your spark plug has gone bad.

First, you’ll need to look at the metal bends that create a gap in the electrodes. Over time, this will deteriorate and appear obviously aged, and eventually, this will cause sputtering. The housing of the plug may also crack and deteriorate, which can cause sputtering as well.

The only way to fix this is to change the spark plug.

Gas Near Lawn Mower_shutterstock_Erica Allin
Image Credit: Erica Allin, shutterstock

6. Dirty Carburetor

If you’ve had your lawnmower for a while, the carburetor could need a good clean. Eventually, deposits can clog it and cause sputtering. However, this typically will not happen until you’ve used it for a while. Carbonators are not something that easily become dirty.

To fix this issue, you’ll need to clean the carburetor. Sadly, this is not always very easy, depending on your lawnmower. In many cases, cleaning your carburetor can be nearly impossible, especially on cheaper lawnmowers that were never made to be worked on.

You’ll need to check your manual for information on how to clean your lawnmower completely, including the carburetor.

7. Bad Gas Cap

If your gas cap no longer vents properly, it can cause sputtering. In this case, the air getting inside your gas tank will not be the correct amount so your mower will not start properly. With that said, this is rarer than other options, which is why we have mentioned it towards the bottom.

Fixing this problem is pretty easy—you’ll just need to replace the gas cap.

cropped man mowing lawn with lawn mower
Image Credit: Pexels, Pixabay

8. Carburetor Issues

There are many carburetor problems that can cause your mower to sputter. Often, these cannot be fixed without professional help. Therefore, these problems are much more difficult to fix than the other options on the market. In many cases, these fixes are so expensive that it is often cheaper to purchase a new lawnmower instead of fixing your old one.

Because these problems differ, we cannot provide any quick fixes. Basically, your hope is that one of the above fixes stops the sputtering. If the carburetor appears to be a problem, then you’re mostly out of luck.

tool divider


There are many lawnmower problems that can cause sputtering. Luckily, many of these problems are very fixable. In many cases, all you’ll need to do is clean off your lawnmower or change inexpensive parts, like your gas cap. It’s when parts like the carburetor fail that you’ll usually run into more serious problems. Usually, this means that you’ll need professional help, which is beyond the scope of this article.

With that said, most fixes are quite easy and straightforward.

Featured Image Credit: Skitterphoto, Pixabay


Related posts

OUR categories

Project ideas

Hand & power tools