lawn mower sputtering

Lawn Mower Sputtering (Why + How To Fix)

You’d like to think that getting your lawn mower started wouldn’t be a trying task. But with a petrol engine, you are going to experience problems along the way but that doesn’t mean you should have to down tools. If you’ve got a sputtering lawn mower engine then you’ve probably wondered what’s causing it.

There are several problems that could cause your lawn mower to sputter. It could be related to clogged filters, worn or dirty parts, moisture in the fuel tank or even a clogged carburetor.

But don’t worry; if your lawn mower is sputtering then this guide will provide you with all of the answers you’ll need. We’ll go through possible problems and how you can fix them.

When your lawn mower starts making that unmistakable spitting sound, this suggests that there is something wrong with one or more of the parts. Generally speaking, this is a good indicator that it’s time to perform some maintenance.

Clogged Fuel Filter

The fuel filter on your lawn mower is going to gather dirt over time; there’s nothing you can do to stop this. But the problem comes when you don’t take the time to clean your fuel filter and this could be the cause of your lawn mower sputtering.

If the fuel filter is clogged then it becomes extremely difficult for the gas to get to the engine and when there isn’t enough fuel, the mower will struggle to run properly. When the air and fuel balance is not spot on, this can cause that sputtering sound.

How To Fix It

When your fuel filter becomes clogged and dirty, you can solve the problem by simply replacing this inexpensive part.

Clogged Air Filter

As well as having a dirty or clogged fuel filter, the lawn mower may also have a clogged air filter which is another common reason for a sputtering lawn mower engine.

In this case, you’ll usually find that debris has gotten into the holes that go from the fuel filter and carburetor and this debris will prevent the smooth flow of fuel to the engine.

clogged air filter

How To Fix It

If your air filter is dirty then you have two options; you can either clean it or you can replace it. But this largely depends on the type of air filter your lawn mower uses.

If yours has a foam air filter then this can usually be cleaned using warm soapy water. There will come a point that it does need to be replaced but once cleaned, they are reusable for some time.

However, paper filters cannot be cleaned this way and while you can bang some of the dirt away, this usually isn’t enough so you will need to replace the filter.

Old Or Wrong Fuel

It is possible to buy the gas that is sold in your local gas station but this usually contains high levels of ethanol. The problem with this is with how quickly it burns and this can be a cause of your lawn mower sputtering.

What’s more, if you use ethanol fuel that has been sitting for a long time, this can make matters worse. As a rule of thumb, you don’t want to use gas that is more than 30 days old as it just won’t perform as well.

How To Fix It

Always make sure that your mower is loaded with fresh, low ethanol gas. If the gas has been sitting idle for some time, you can add a fuel stabilizer.

Damaged Or Faulty Spark Plug

Spark plugs are not the most common cause of a sputtering lawn mower but they could be the problem. When they are, it is typically because the spark plug is dirty or damaged. So, make sure to check them when you are troubleshooting.

When the spark plug is damaged or worn, this can make it incredibly difficult for the engine to start. Moreover, even a dirty spark plug can cause issues so this is another part you’ll need to make sure is kept clean.

Bad Spark Plug

How To Fix It

The good news is that this is an easy fix. If it’s simply a case of a dirty spark plug then use a wire brush to clean it and see if that solves the problem.

For damaged spark plugs, you can buy a replacement for as little as $8, so it’s super affordable. Plus, they’re easy to replace. That said, we would recommend routinely replacing the plug every couple of years.

Clogged Carburetor

The carburetor can become clogged with gunk over time and this is unavoidable since the residue is a byproduct of combustion. However, if this is allowed to build up and is not removed, it will prevent the mower from running correctly.

How To Fix It

The great thing about this is that you can easily clean the carburetor using a carburetor cleaner which is sprayed inside and will loosen that dirt. It’s good practice to use the cleaner whenever you are maintaining your mower to keep things running smoothly.

Moisture In Fuel Tank

It probably doesn’t take a genius to figure out that moisture isn’t welcome in a combustion engine. Take a look by removing the gas cap and checking inside the tank. If the fuel looks as though it is separating then this could be the cause of your problems.

How To Fix It

You will need to drain the gas tank of all liquid and add some fresh fuel. Once any old gas residue has gone through the fuel lines, your problem should be fixed.

Dirty Mower Deck

Think about the conditions you have been cutting in. Is the grass very long or perhaps wet? If so, this could be the issue as the clippings will become caked to the mower deck.

how thick should a mower deck

How To Fix It

Disconnect the spark plugs and tip your mower over to check the state of the deck. If there is a build up of grass and debris, take the time to clean this and your lawn mower should stop sputtering.

Lawn Mower Sputters Then Dies

When a lawn mower sputters, this is usually a sign that something is wrong. When the mower is in full working order, it should run smoothly and without any issues.

The engines in gas lawn mowers rely on many different parts and it takes just one of these parts to malfunction for the whole operation to fail.

If your lawn mower sputters then dies and none of the issues we have discussed in this guide fix the problem, it might be time to take your machine to a professional. They can perform a more detailed assessment and fix any related issues.

Lawn Mower Sputters When Blades Are Engaged

Have you noticed that your lawn mower sputters then dies while the blades are moving? If so, this is usually related to one of three parts.

Belt

The first issue could be the belt which is a common cause of a lawn mower sputtering when the blades are engaged. Typically, this is to do with the belt routing.

Toro TimeCutter Drive Belt

How To Fix It

Start by removing the belt guard and setting the deck to the lowest height. Now, take out the rear deck pins and bring the belt up over the pulley.

You can slide the deck from out of the mower and take a look to see if the belt routing is faulty. If it is then you will need to follow the advice in your owner’s manual to reroute the belt.

Pulley

Sometimes, the pulleys can stick and this will cause your lawn mower engine to sputter. In a correct setup, the pulleys should be engaged by the drive belt but as before, you will need to do some troubleshooting to find out if this is the issue.

How To Fix It

Make sure that you start by removing the belt from the pulley. You can then engage the blades before spinning the pulleys manually to see if they turn. There should be an accompanying low pitched sound but if not, then this suggests damaged pulleys which will need to be replaced. Unfortunately, this is not usually a job that you can do at home.

Safety Switch

Another common issue for a mower to sputter while the blades are engaged is the safety switch. This switch is designed to shut the mower off in an emergency situation such as if the mower tips over. But sometimes, it can malfunction and shut off the mower when nothing is wrong.

makita safety pin

How To Fix It

If you are having this problem then you will first need to remove the seat from its bracket and locate the safety switch. Once you have done this, take a look to see if there is any visible damage. You might not be able to see anything so testing with a multimeter is a good idea.

It should read 0 ohms but if not, then this suggests faulty switch which you will need to replace.

Why Is There White Smoke While Sputtering?

White smoke can be a worrying sight but this, as well as blue smoke, could be a suggestion that there is an oil spill within the mower’s engine. The best way to solve this problem is simply to allow the oil to burn off. Once it has, the white smoke will stop.

However, it is important to try to reduce the chance of an oil spill. When you are performing maintenance on your lawn mower and have to tilt it onto its side, be sure to do this so that the carburetor is facing up.

Final Thoughts

Lawn mowers can be pesky tools at times and if you’ve noticed that you have a sputtering lawn mower, it can be wildly annoying. But the good news is that there are several easy to fix issues that are likely the cause.

It’s unlikely that there will be a serious cause for this problem but if you are in any doubt, be sure to seek professional advice.

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Andrew Fisher

Andrew Fisher

Andrew is a dedicated father of three who really takes pride in his lawn and garden. You'll find Andrew behind the scenes of almost everything Edge Your Lawn produces. When he's not helping readers find all the information they need, he's in his backyard working on his lawn and garden landscaping. This year he hopes to build an outdoor deck and sort out his veg patches.

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