May 8, 2021
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Lawn Mower Sputtering? Check THESE 3 Things FIRST!
Is your Lawn Mower Sputtering? Don't worry, you're not the first person to have that issue. The lawn mower typically takes more abuse than almost any other outdoor tool, so this is no surprise AND I'm pretty sure I can help you fix it on your own!

Running year after a year through high grass and coarse weeds, hitting against the rocks, dirt mounds, doggy bones, and similar obstacles certainly take its toll on the mower's well-being. In addition to this beating, a lot of owners skip maintenance actions and improperly store their machines leaving them at the mercy of rain, humidity, or heat.

So, although some believe that they will work forever, every lawn mower eventually breaks down and you'll need to repair it or replace its parts.

Some malfunctions require professional help and expertise but, luckily, you can take care of plenty of problems by yourself.

Lawn mowers are not overly complicated machines and their small engines feature a limited number of parts. Their operation principle is fairly simple and more often than not you'll be able to use your average homeowner's technical skills to diagnose and rectify the problem.

One of the most common issues lawn mower users face is that their engine starts to sputter while making rounds around the lawn.

The engine running rough and "coughing" can sometimes be a symptom of a more serious underlying engine malfunction, but, usually, it's an easily solvable matter that you can handle without any extra help.

Here's something you DON'T want to hear:

Lawn Mower Sputtering is mostly just the indicator of improper maintenance and can be easily avoided by following the instructions and performing regular checks.

To run smoothly, the engine needs:

  1. Fresh fuel
  2. A flow of clean air
  3. And the ignition spark.

So, if your lawn mower sputters, the culprit can usually be found within these three processes.

Sputtering Lawn Mower? Check These 3 Things

If you let your guard down and allow dirt or bad fluids into the system, your engine will not only sputter but in time it may fail to even start or eventually die completely.

At that point, you'll have to turn to experts, or pony up the cash for the new engine.

When trying to figure out the cause of sputtering, you should start with the simplest and most obvious ones.

If you make sure that everything is in order there, but the engine still struggles, move on to the next step until you have exhausted all of the options within your expertise level. Below, we listed all of those steps related to the most probable issues causing the lawn mower to sputter.

1.) Check the Fuel System

Sputtering Lawn Mower
One of the most common reasons for the faulty engine operation is the bad batch of fuel inside of your tank.

This is good news since it's also the easiest issue to solve.

Try to remember when the last time was you filled the gas tank. If it was more than thirty days ago or even at the end of the previous mowing season, then the old gas is the probable suspect for your troubles. Here's Why:

  • Organic components within gasoline can quickly evaporate, making the old gasoline burn faster and rendering it useless. Your mower's engine probably has only one cylinder making it more sensitive to these issues than the ones found in cars with four or six cylinders.
  • The speed at which gas goes stale has a lot to do with the ethanol percentage it contains.

Always look to buy gas with less than 10 percent of ethanol, or, in the best case, completely ethanol-free.

  • Ethanol burns so hot that it can even damage some of the plastic parts. It also helps create water residue within the reservoir and that is definitely not good for the engine.
  • Water in the tanks can also come from condensation, or faulty and loose gas cap, especially if the lawn mower isn't properly stored and protected from rain and humidity. If the water enters the cylinder it hinders its functioning.
  • If you determine that you have faulty gasoline in your tank, drain it and dispose of it responsibly.
  • Before you pour in the fresh batch of gas, shake your tank a little. Sometimes, an outside object can make its way to the tank and restrict the fuel flow by clogging the exit hose.

If the engine experiences gas flow stoppages, it will struggle and sputter. Another issue that can influence the proper gas flow is clogged fuel filter. Remember to check it and replace it if needed.

Besides the one on the tank exit, the fuel system contains at least one more filter and a network of hoses and openings.

If any of them is clogged, the supply of fuel for combustion will not function in a way needed for the engine to run steadily.

So,make sure to also check the lines connecting tank, carburetor, and cylinder, as well as the fuel pump which is usually mounted on the carburetor. If they are dirty, try to clean them or, if that doesn't work, replace them.

2.) Inspect the Ignition

Lawn mower sputtering can often indicate the issues with ignition. And these issues can usually be traced back to the spark plug.

A damaged or loose spark plug is often associated with starting problems, but it can also cause the engine to struggle and run poorly. If it's dirty or corroded with residue, the plug can no longer properly spark the fuel and set the engine operation in motion.

Here's What You Should Do:

1.) Remove the spark plug using the spark plug wrench and check the firing tip to see if it's clean. 

2.) You can clean oily buildup with an old rag or use a wire brush (or sandpaper) if it's fouled with carbon.

3.) Use the spark plug gauge to measure the spark gap and see if it's set to the distance described in the instructions.

4.) The wrong gap setting will cause issues with the engine running and quickly create a carbon buildup.

If the ceramic housing is damaged, or the tip of the electrode is rounded over, you should replace it with a new one.
Lawn Mower Spark Plug
Since the spark plugs are rather cheap, it's a good idea to always have at least one spare lying around. When placing the spark plug back to the socket make sure not to overtighten.

If the spark plug issues persist, consider switching to a different brand. Besides emergency replacements, make installing a new spark plug a part of your yearly lawn mower maintenance.

By the way, you can get Lawn Mower Spark Plugs and just about anything else you need on!

3.) Adjust or Clean the Carburetor

Once it receives the supplies of air and fuel from other components, the carburetor's job is to mix them properly to make the engine run. If the mixture is a bit off, the engine will sputter and struggle to maintain operating efficiency. Eventually, it may even die.

Although the carburetor usually performed poorly because it's clogged and dirty, it is possible that it just needs some adjustments:

  •  Adjusting the idle and low-speed setting on a carburetor is fairly simple. Each setting is controlled by a dedicated screw, usually clearly marked.
  • Opening these screws just a tiny bit increases the fuel flow to the carburetor and helps the engine run smoothly at these speeds (or at idle). 

Bear in mind, if the carburetor is dirty, this is just a quick and temporary fix.

The body of a carburetor contains jets, springs, floats, and needle valves, all of which are extremely minuscule and sensitive.

Sticky by-products of the combustion and fuel residue can create gunky buildup over these components preventing them from performing their function to the fullest.

If one of these gunky deposits breaks off, it can float through the system, clogging it and causing the whole engine to sputter. The sensitivity of carburetor parts is the reason why the tinkering with the carburetor is usually best left to the professionals.

Still, there's some cleaning you can try on your own to see if you can make your lawn mower stop sputtering.

Carburetor cleaner sprays can be bought at any better-equipped store and you can use it for regular preventive maintenance.

Spraying it directly into the intake helps dissolve the deposits and frees up the flow inside the carburetor.

Here's a GREAT Video explaining how to clean it yourself, in just a few minutes:

if you feel you're extra handy, you can try disassembling the carburetor and performing a thorough cleaning. 

Even getting to the carburetor is not a particularly easy task:

Depending on the engine type, you'll probably have to remove the fuel tank, air filter, breather pipe, fuel lines, and manifold seal. 

Carefully disassemble the carburetor and soak it in cleaning liquid.

You should leave it there overnight. In the morning carefully clean all of the components. You can use compressed air to blow through them, but be careful.

While you're at it, consider buying a carburetor repair kit and replacing all of the gaskets. Once you're done, reassemble it, put it on the back on the engine and reinstall all of the components in the reverse order.

Again, if you're unsure about any part of this process, don't even start with it and get the help of an expert. Another option is purchasing a new carburetor and replacing the old one.

What to Do if the Lawn Mower is Still Sputtering?

If none of the above methods work, consider your mowing practices. Letting your grass grow too high before mowing or cutting it while still wet can also burden the engine and cause it to stutter.

See how your mower works when faced with less challenging assignments. And if the problem persists, then there's no other option than taking your machine to a mechanic. If the engine sputter is still present after you've performed all of the steps on our list, then probably have a serious engine issue on your hands.

Whether you try to take care of it yourself or leave it to a professional, the most important thing is to react as soon as you notice your engine sputtering. Continuing to work your lawn mower in that condition can lead to irreversible damage and leave you with no other option other than buying a new one.

Daniel Simmons

About the author brings my 25 years experience as a professional gardener and landscaper to you!

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