Reasons Your Mower Stopped While Mowing

The warm weather and good amounts of rain I’ve received recently have me mowing twice a week. At times, I get busy and fall behind on my bi-weekly mowing. That’s when it happened. I took my lawn mower out and it died while mowing. What am I going to do?  

A lawn mower may stop while mowing because it is not getting the correct air and fuel the engine requires to keep running. A dirty carburetor, plugged air filter, bad fuel or faulty fuel cap can all be causes of your lawn mower shutting off. 

I have helped many customers troubleshoot this issue over the years. Keep reading and I’ll share the most common reasons your lawn mower stopped while mowing the lawn.

I’ll go over items to check on your lawn mower and how to get your lawn mower up and running again. 

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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Reasons Your Lawn Mower Stopped When Mowing 

Bad Fuel

It doesn’t take long for your fuel to break down and become bad. Unleaded gasoline beings to decay after about 30 days. The fuel loses the chemical makeup that allows it to run at its best. 

Much of today’s fuel use ethanol in its makeup. Ethanol is a substance derived from corn to help make our fuels more environmentally friendly. Ethanol does not do any favors to small engines.

In fact, ethanol attracts moisture from the air. When this moisture evaporates, it can leave a gummy residue in your fuel system. This residue can cause your lawn mower to stop while mowing. 

What type of fuel should you use in your lawn mower’s gas engine? You can use a fuel that has an 87-grade octane rating or higher and an ethanol content of 10% or less. Some homeowners choose to pay a little more and use premium fuel or recreational fuel, but it is not absolutely necessary. 

I do highly recommend you use your fuel within 30 days of purchase. If you are not able to use it that fast, you can add a fuel additive called Sea Foam to your fresh fuel to stabilize it and reduce the moisture content so you can make your fuel last a little longer. 

For a more in-depth look at fuel, read my article “This is the Type of Gas Lawn Mowers Use”. 

Dirty Carburetor 

Your lawn mower carburetor is designed to regulate the amount of fuel and air needed to create combustion. A dirty carburetor can cause your lawn mower to die while mowing. The deposits and gummy material left behind when running bad fuel is most often the culprit. 

Most of the time, a dirty carburetor can be cleaned to get it back in working order. If there is excessive buildup, or you just don’t want to clean it, you can always replace it. 

I recommend trying to clean it only if you are mechanically inclined. You will be working with a lot of small parts. If you are not, your local lawn mower mechanic will be able to help you. 

12 Steps to Identify and Clean Your Dirty Lawn Mower Carburetor 

1. Spray carb cleaner to minimize carbon buildup. Remove the air filter and spray some carb cleaner in the air intake. Start the engine to see if it will run. If your mower fires up and still won’t stay running then you need to get inside the carburetor. 
    

2. Gather pliers, screwdrivers, sockets, and ratchets so you don’t destroy parts while taking the carburetor apart.  
    

3. Take a photo for reassembly. These days most people have a handy camera on their phones. It’s a very good idea to take a picture of the carburetor so you can refer to it if you don’t remember how to reassemble it after tearing it apart. You will want to make sure you get a photo showing how the linkage and springs go back on the carburetor. 
    

4. Remove the throttle cable and choke cable if your mower has one. 
    

5. Undo the filter housing and nuts or screws that hold on the carburetor. 
    

6. Slowly remove the springs so you don’t stretch them out too much. You may have to twist the carb a bit to get the springs off. Also, watch the gasket at this point so you don’t tear it. This is the gasket located between the engine block and the carburetor. 
    

7. Remove the bottom screw from the float bowl. The float bowl is where gasoline is stored inside the carburetor. It should have gas in it so have a rag ready to catch the gas. 
    

8. Remove the bowl being careful to not damage the o-ring around it. Caution: Do not get any carb cleaner or any other chemical on the o-ring. It will stretch out and you won’t be able to reuse it. 
    

9. Inspect the stem for clogged holes. This stem hangs down from the center of the carburetor and has holes in it. If these holes get plugged from old fuel it will not draw fuel up to the jet. If the holes are plugged, take a thick wire to clean them out. It’s easier to see what you’re doing if you use a flashlight. Once you get the holes clean you can rinse them with carb cleaner. 
    

10. Inspect the carburetor for hard crusty white buildup. This white buildup is fuel additives including ethanol. You need to try to get as much of the white power material out as you can. It’s nearly impossible to get it all out. 
     

11. Reassemble the carburetor now that the carb is clean. Put it back to together in the reverse order you took it apart. Remember to refer to the photo you took of the carburetor when reassembling so all parts are reinstalled in the right places. 
     

12. Add fresh fuel plus a fuel stabilizer before you start your mower. Pour the fuel into the tank and give it a chance to fill the bowl of the carburetor. Start your engine. If you are starting with a pull cord, give the rope a yank. It may not start on the first pull, but it should start after several pulls and continue to run. 

Broken or Clogged Fuel Cap 

A simple item like a broken fuel cap can be the reason your lawn mower stops while mowing. Fuel caps are designed to vent allowing air through the cap. When a cap is broken and will not vent, a vacuum is created in the fuel tank that restricts the flow of fuel. 

Check to see if the fuel cap is bad by taking it off and running your mower. If your mower no longer dies while mowing, this may be your problem and you will need to purchase a new gas cap. 

Be careful not to let any dirt or debris enter the gas tank while your cap is off. Run your mower without the mower deck engaged so you are not stirring up a bunch of dust and grass. 

Only run without a cap to perform the test. Replace with a new cap if needed. You do not want to mow without the gas cap or leave your leave the gas tank cap off. Doing so can allow debris and water in the fuel tank.

Clogged Air Filter 

A plugged air filter restricts the amount of air to the engine. Without clean air, the engine is not able to run. You should check your air filter frequently to make sure it is not plugged with dirt and debris.

When checking your filter, take it out of the air filter housing. Tap the paper filter against a hard surface to knock out any loose dirt.  

Hold the filter up to a light and make sure you can see light through the filter.  If you cannot, replace the air filter.  To learn about cleaning other types of filters, read this article. 

You can cause significant engine damage when running a plugged air filter. When your engine isn’t able to pull clean air through the filter, it begins to run very hot and often overheats. 

Too Much Engine Oil

Adding too much oil to your lawn mower can cause your engine to smoke and stop while mowing. The smoke can clog your air filter causing your engine to look elsewhere for air. 

Too much oil in your lawn mower can cause significant damage including internal engine damage and the possibility of having to replace your engine. 

Check for Other Fuel and Air Restrictions in Your Lawn Mower

Always check for fuel and air restrictions when checking for reasons your lawn mower stopped when mowing. If none of the items listed above solve your problem it is always good to look at other possibilities of an air or fuel restriction such as plugged fuel lines or a bad fuel filter.