Lawn Mower Sputtering? Here’s How to Fix It

Lawnmower maintenance is a crucial part of keeping your mower running properly. Regular maintenance promotes the overall health of your lawnmower and its ability to properly operate.  But even with regular maintenance, there may be times when you experience issues with your mower.  One common problem among lawnmowers is sputtering.  Lawn mower sputtering is generally an inexpensive and easy fix that can be done on your own as part of your regular maintenance.

In this article I’ll share what causes a sputtering lawn mower, and what you can do to fix this common problem.

Let’s get to it!

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About Lawn Mower Engines

The engine of your mower relies on the right combination of fuel, air, and a spark (for combustion).  Your mower needs each of these to prevent the mower from sputtering and eventually dying. 

For the most part, many of the issues that cause a sputtering mower can be fixed by the weekend warrior. 

However, there are times when it is best to use a professional for the job.

You’ll want to check a few items to determine what’s causing your mower to sputter, and that will determine if it’s a DIY fix, or you need to call in a professional.

Let’s look at some reasons why your lawnmower may be sputtering and how you should address each of these issues. 

Identifying the Cause of a Sputtering Lawn Mower

Below are some of the more common reasons for sputtering lawnmowers and how they can be resolved.

Old Fuel or the Wrong Fuel

The gas you get at the local gas station will generally contain about 10% ethanol. It’s cheaper than pure gasoline, and works fine for cars, but I don’t use it in my mower because it’s low quality.

Ethanol burns quickly and can potentially melt plastic parts, leading to sputtering in your mower. And if you use ethanol blended gas, only buy a little at a time.

If it sits in your garage for more than a couple of months it will go bad and can lead to a sputtering mower.

You can use a fuel stabilizer to extend the life of the gasoline, but I recommend using an ethanol-free gas. It’ll burn cleaner and help your mower to start on the first pull and roar like a tiger.

I use 4-cycle Tru-Fuel in my Honda mower, and love it. It’s pricey, but I highly recommend you try it. You can buy it locally at most box stores, or you can order it online (Amazon link).

Clogged or Dirty Air Filters

Dirty air filters are one of the most common reasons lawn mowers sputter.

Dirt can be present in the apertures that lead from the carburetor and the fuel filter and interrupt the flow of fuel supply to the combustion chamber. 

You want to be sure to clean or replace dirty air filters. 

Paper air filters will need to be replaced. But you can generally clean foam air filters with a drop of liquid dish soap and warm water.

After cleaning the air filter, squeeze dry and air dry.

My Honda mower uses a paper air filter which I replace every year as part of my spring mower tune-up.

During the summer, I remove it and blow the dust and debris off before each mow.

Dirty Fuel Filters

Any filter will get dirty with time, and just like the air filters, fuel filters in a lawn mower need to be clean.

Replace yours if they’re dirty.

Clogged fuel filters prevent the flow of gasoline to the engine which can lead to a lack of fuel needed for proper functioning.

This imbalance of air and fuel in your engine can cause your mower to sputter and run rough.

A Bad Gas Cap

Misfires can occur with an improperly vented gas cap on your mower.

If your gas cap has improper venting, too much air can be allowed to enter the gas tank (or too little). This can cause a vapor lock.

It’s an easy fix – just replace the cap if it is damaged or bent or if you see that the vent hole is restricted.

That Carburetor is FILTHY

Gunky deposits can occur in the apertures and carburetor.

This buildup is from the sticky by-products of hydrocarbon and combustion. 

Using a carburetor cleaner spray (this one on Amazon is what I use and swear by) on a regular basis can loosen dirt deposits and keep your mower’s apertures and hoses clean.

I give my carb a shot every time I clean my air filter before I mow.

Water in the Fuel Tank or Fuel Line

Water prevents the mower cylinder from properly igniting.  Remove the cap and check the gas tank for evidence of water (if you see the liquid separating or looking like two different colors). 

If there is water in your tank, siphon or drain it, then add new gas.

After old gas in the line works its way through the mower’s engine it should stop sputtering and run like new again.

Check the Spark Plug

Worn or damaged spark plugs make the engine difficult to start.  If the plug is damaged, worn, or deteriorating you should replace the plug. 

If the tip is fouled or dirty, just clean it with a wire brush and reset to the mowers manufacture’s settings. 

You can also look into purchasing another brand of spark plug to see if the mower runs better with a different brand. The plug that comes from the factory with some mowers doesn’t work great on some lawn mower brands.

The spark plug is generally not the first thing I’ll check for a sputtering mower. But a dirty or damaged plug can sometimes be the cause.

Your spark plug is an easy item to replace, and costs about $8 at your local hardware store.

I replace my plug every other year as part of my annual maintenance routine. If it has been more than two years since you’ve bought a new plug, I recommend replacing it as part of your tune-up to fix your sputtering lawn mower.

Your Carburetor Has Issues

Some carb cleaning spray will help if your carburetor is simply dirty, but sometimes there are other issues that can cause lawn mower sputtering.

The carburetor affects how well the mower runs. The wrong blend of air and fuel can cause the carburetor to run rough. 

The carburetor must have the right amount of air and fuel to run correctly, and while the average weekend warrior can probably find and remove his mower’s carb, due to its complexity, the carburetor can be tricky to clean or repair.

If you’ve tried everything else on this list, it’s likely a carburetor issue and your mower may require professional service. 

A professional can determine the repairs, cleaning, and replacements needed. They’ll then get the carburetor working properly.

First, check to see if your mower is covered by a warranty of any kind. If it’s not, find a local small engine repair guy (or gal), and have your mower serviced.

It’ll be cheaper than you expect.

A Dirty Mower Deck

Caked grass on the mowing deck can cause the mower to sputter. 

If you have tall or wet grass you may have noticed that your mower started sputtering as you mowed your lawn.

Check the underside of the mower for excess grass caked on. 

Use a wrench to remove the spark plug to prevent the mower from turning on while you work. Then scrape the excess grass using a scraping tool such as a paint scraper.