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Why Is My Riding Mower Sputtering?

Why Is My Riding Mower Sputtering?

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Willie Moore
Latest posts by Willie Moore (see all)

Have you ever taken your lawn mower out to mow the grass, only to find that it sputters and then stops? It’s frustrating, especially if you just filled up the gas tank with fuel. Still, you may start to wonder why your riding mower is sputtering.

Your riding mower can sputter due to using a bad batch of fuel in the tank, a damaged gas cap, clogged air filters, excess grass under the deck, a damaged spark plug, a clogged carburetor, or water in the fuel tank. These factors tend to cause your mower to lose power, leading to sputtering.

Read on for more details on these and insights into how to fix them.

Common Causes of Sputtering in a Riding Lawn Mower

As I mentioned, the common causes of sputtering in a riding lawn mower share one feature in that they reduce the machine’s power, leading to a deterioration in performance. In general, they result from either neglect or failure to regularly inspect and replace any damaged parts.

Here’s an in-depth discussion of these factors.

Bad Batch of Fuel Inside the Tank

When you took your gas can inside the store, did it smell like gasoline?

Even if there isn’t a sign warning not to fill up your can with old fuel, make sure that the gas is fresh before using it in the machine. Gas that contains ethanol left sitting for a long time (over 30 days, as a rule of thumb) will go bad and cause your mower to sputter.

See Does Ethanol-Free Gas Go Bad? Fuel Shelf Life Comparisons.

The Gas Cap Is Damaged

If the gas cap is damaged, gasoline will leak from the tank as you mow, making it hard for your mower to have sufficient power. This might happen if the gas cap isn’t closed all the way or if it’s missing. 

A damaged gas cap can also cause gasoline to evaporate, which is why it’s crucial to replace it.

See Lawnmower Spits Gas Out of Fuel Cap: Reasons and Fixes.

The Air Filter Is Dirty or Clogged

If your air filter is clogged, there won’t be enough air getting through for proper combustion. This leads to poor performance and possibly even a broken engine.

A clogged air filter can be caused by leaves or twigs getting in there, although it might also cause the mower to sputter if the filter is dirty for other reasons.

There’s Excess Grass Under the Deck

When your deck gets clogged with grass, your mower won’t have enough horsepower to cut through thick patches of grass. Excess grass under the deck is a common reason for this problem. In addition, if the grass is very thick, it can get caught in the blades, which will also cause your mower to sputter.

Also, it would help to note that lawnmowers sputter when the blades are engaged.

Note: If your lawnmower starts sputtering when you’ve engaged the blades, it’s likely that there’s something lodged in them. Only engage the blades if you’re sure that everything is clear under them, or else you may damage the engine.

The Spark Plug Is Damaged or Loose

A spark plug is a small device inside your lawnmower that sends out an electrical charge to start the combustion process and keep it going. If the spark plug isn’t working because it’s loose or damaged, you might have a hard time starting the mower, and it might sputter before running.

See Here’s How to Know if a Lawn Mower Spark Plug is Bad.

The Carburetor Is Clogged or Dirty

Like a car’s carburetor, your lawn mower’s carburetor is responsible for getting the right amount of gas into the engine so it can continue to run. It can get clogged with dirt or debris if it’s dirty, which will affect its ability to perform.

A clogged carburetor can lead to your mower sputtering and catching on fire. Make sure that the carburetor is cleaned before you start up the machine again.

Water in the Fuel Tank or Fuel Line

If there’s water in the gas tank or fuel line, it could be blocking the passage of gas and therefore affecting your mower’s ability to continue working.

If you’ve recently used a pressure washer near your ride-on lawnmower or if there was a sudden storm that caused puddles on the ground, water could have made its way into the fuel tank or fuel line.

How To Prevent Your Riding Mower From Sputtering

Now that you have some insights into what causes a riding mower to sputter, you might want to know how to prevent that from happening. So, how do you go about it?

Here are some ways to prevent your riding mower from producing those spitting sounds.

Replace the Old Fuel

If you can’t remember how fresh the fuel in your lawnmower is and it has been a while since you used it, replace it. The best way to do this is by buying fresh, new gasoline and adding it to your tank. Also, ensure any gasoline in the tank doesn’t stay for more than 30 days.

However, you can put in a stabilizer if you’re storing your mower over the winter, as this keeps your gas fresher longer.

Replace the Gas Cap

Ensure the gas cap is on securely so that no gasoline can leak out of your tank. You might need to replace it if it’s damaged since this could cause leaking.

Caveat: Ensure the replacement meets manufacturer specifications to ensure it fits your mower.

Replace the Air Filter

You might want to replace your lawn mower’s air filter frequently, at least every three months. This will ensure that it continues to run smoothly and won’t sputter or spout because of damage.

If you’re not sure what size your filter is, check the manual for your ride-on lawnmower.

Clear the Deck of Grass and Deck

Remove any excess grass from under your deck before you start up your mower again. 

Many riding lawn mowers have a small tool for this purpose just below where you fill up with fuel, but some do not, or yours may be broken. If this is an issue, use a garden hose or a stick to remove any grass bunches underneath the deck.

Replace the Spark Plug

The spark plug is critical to the functioning of your mower, and loose or damaged ones can affect how it runs. Therefore, replace the spark plug before you start up your mower again. This will ensure that your mower runs smoothly and won’t sputter.

Clean the Carburetor

If you know your carburetor is dirty, make sure to clean it before using your lawnmower again. If you’re not sure how to do this or don’t know whether or not your engine has one, check your manual for steps on locating and cleaning the device.

Also, this video will come in handy to ensure you get the best results:

Lawn Mower Repair : How to Clean the Carburetor on a Lawn Mower

It should run much more smoothly than before. If not, keep troubleshooting.

Rid the Fuel Tank of Water

If you notice water in your gas tank or fuel line, let it dry out completely before using your lawnmower again. To get rid of the excess water, you can drain the gasoline and leave the cap off for a while to allow air inside. I tend to empty it then flush the tank with another half-gallon or so just to make sure all the water is gone.

The Bottom Line

To prevent your ride-on lawnmower from sputtering, replace the old fuel, gas cap, air filter, and spark plug as soon as possible. If you notice any of these pieces are loose or damaged, fix them immediately to avoid future problems.

Additionally, make sure your deck is clear of debris before using your ride-on lawnmower and clean the carburetor if needed. By replacing old parts and following these tips, your ride-on lawnmower should run smoothly again in no time!

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