Why Does My Lawn Mower Sputter? 8 Causes and Solutions

Lawn mowers are prone to all sorts of mechanical errors, especially once they get a bit too old. However, there’s no need to toss your mower just yet. Sputtering is much more common than you think, and it’s not always a cause for a new mower.

Your lawn mower sputters because of excess amounts of moisture, clogged filters, or malfunctioning spark plugs. Other causes include using an incorrect type of fuel, bad gas caps, and a dirty mower deck.

Throughout this article, you’ll also learn the following info about why your lawn mower sputters:

• Different causes of a sputtering mower
• How you can fix each issue and prevent it
• Different tips to keep your mower lasting longer

What Causes My Lawn Mower To Sputter?

Lawnmower maintenance is essential to ensure that your mower has a longer life and runs properly. Nevertheless, lawnmower issues may be experienced even with regular maintenance.

Sputtering is a common problem while using a lawnmower. Sometimes the mower coughs, sputters, and stops working. Other times it restarts only to fail again.

In most cases, this is generally an inexpensive and easy-fix problem that can be solved by an individual as part of a maintenance routine. However, a few are left to professionals.

Lawn Chick points out that you need to identify the cause of the sputter before you try to fix it.

Here are some of the causes of sputtering in lawn mower:

Clogged or dirty air filters

Dirty or clogged air filters block fuel supply flow into the combustion chamber. This is one of the most common causes of sputtering in lawn mowers. Dirty air filters should be cleaned or replaced. Dirt at times can be found in the openings that lead from the carburetor and the fuel filters.

Wrong or old fuel

The mower engine relies on the right combination of fuel, air, and a spark to allow combustion. The gas found at a local gas station contains about 10% of ethanol. It’s cheaper than pure gasoline, and although it works efficiently for cars, it’s not the best quality for a lawn mower. Ethanol burns quickly, leading to mower’s plastic parts to melt, causing your mower to sputter. Old fuel that has not been in use for a long while can go bad and cause your mower to sputter.

Dirty fuel filters

Just like air filters, fuel filters get dirty too over time. Your fuel filters must be clean, and replacements should be made when they get too dirty. Clogged fuel filters prevent the flow of gasoline to the engine, causing an imbalance on the right combination of properties necessary for the smooth functioning of the lawn mower. This imbalance leads to sputtering.

Water or moisture in the fuel tank or the fuel line

Water may come from condensation, a loose gas cap, or it may have been in the gas containers before it got to your mower. It prevents the mower cylinder from properly igniting.

To check if the sputtering is due to water in the fuel tank, remove the cap and check the gas tank for evidence of water. If the liquid separates or looks like it has two different colors, this could be the problem.

Water damage can quickly ruin a lawn mower. Try to change the fuel as soon as you can after a rainstorm if it’s flooded.

A bad gas cap

Usually, misfires occur when your mower’s gas cap isn’t properly vented. This causes either too little or too much air into the gas tank leading to a vapor lock.

Dirty carburetor

Hydrocarbons, which are by-products of combustion, tend to cause a buildup of gunk deposits in the carburetor, causing a blockage in the apertures leading to sputtering of the lawn mower. 

Poor, Worn or damaged spark plug

A damaged, worn, or imperfect spark plug can make it difficult for the mower to start. Check the spark plug’s firing pin and clean it with a wire brush if it’s dirty. If it’s worn out, consider replacing it.

Dirty mower deck

You may have noticed that your mower sputters when mowing tall or wet grass, the mower sputters due to caked lawn on the mowing deck. You should check the underside of your mower for excess grass caked on it.

For more maintenance issues and fixes relating to a mower deck, check out this article.

How To Fix It

Many of the issues that cause a lawnmower to sputter are an easy-fix, but in some cases, it’s best to involve a professional for the job. The following are various ways to fix your mower so that it doesn’t sputter:

1. Inspect for signs of water in the gas tank. As Hunker suggests, you should siphon or drain water from your tank by tilting the machine over, catching the gas in a plastic container, and then pouring it in new gas. The mower will stop sputtering after the old gas in the line works its way through the mower’s engine.
2. Replace or clean dirty air filters. Foam air filters can be cleaned with liquid dish soap and warm water. After cleaning the air filter, squeeze dry and air dry. As for the paper air filters, you should replace them. Remove the air filters, blow the dust and debris off before each mow for maintenance purposes.
3. Check the underside of the unit for caked grass. Remove the spark plug using a wrench to avoid the mower turning while you are working on its undercarriage. Proceed to scrape off the grass using a paint scraper.
4. Replace a cap that’s damaged or bent or if you find that the vent hole is restricted.

Preventive Tips and Tricks

There are few tricks or ways to prevent sputtering in your lawnmower during use, and it all trickles down to proper maintenance. Below are a few tips on how you can ensure your lawnmower runs for a long time:

• Use fuel stabilizer or Ethanol-free gas. A fuel stabilizer aids in extending the life of the gasoline. It’s recommended to use an ethanol-free gas to burn cleaner and help your mower start on the first pull.
• Replace dirty fuel filters to facilitate the flow of gasoline to the engine. These can also cause your mower to blow white smoke.
• Use carburetor cleaner spray to loosen up dirt deposits as it keeps your mowers apertures and hoses clean when cleaning the carburetor. Too much carbon clogs the carburetor.
• Remove the spark plug and examine the firing tip (this is where a bend of metal creates a gap between it and the electrode). If the firing tip is covered with carbon, then clean it using a wire brush and reset the difference to the mower. Replace the spark plug if the porcelain housing is cracked or chipped. If the electrode’s tip is rounded over or if the metal bend has deteriorated, then it’s time for a replacement.
• Clean and replace air filters regularly to avoid interruption of airflow into the combustion chamber.

Final Thoughts

It’s no secret that your lawn mower shouldn’t be sputtering. There could be a variety of causes. Once you’ve identified the issue, do your best to fix it as soon as possible.

As a final tip, don’t feel ashamed to rely on professional help. It’s always a better idea to pay an expert to get the repair done without getting yourself in trouble.

You never know when a simple problem could be a cheap repair rather than getting a brand-new mower.