8 Reasons Your Lawn Mower Won’t Stay Running


What happens when your mower won’t stay running once you finally find time to mow your lawn? Pure frustration. Having to troubleshoot and fix your mower when you’re short on time can leave you feeling deflated.

A lawn mower won’t stay running when it doesn’t receive the air, fuel and spark it requires. This can be due to old fuel causing fuel restrictions in the fuel line, fuel filter or carburetor. A plugged air filter, dirty spark plug, bad ignition coil, clogged fuel cap or an incorrect choke setting can also cause a lawn mower to stop running.

Performing routine maintenance on your lawn mower can help prevent this issue. I’ll go through the different reasons your mower may just quit in the middle of your lawn so you can get back to mowing.

Lawn mower won't stay running

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Reasons Your Lawn Mower Won’t Stay Running

Bad or Old Fuel in Your Lawn Mower

Running bad fuel or fuel that has been sitting around for a long time can have negative effects on your mower. Fuel becomes less stable and attracts moisture from the air. This can cause corrosion in the fuel system.

The ethanol and moisture in the fuel system will leave behind gummy deposits that will clog the fuel system preventing fuel from getting to the engine. Read more about the right type of gas to use in your gas-powered lawn mower here.

Fuel Restriction in Fuel Components

This gummy solution left behind, when the moisture evaporates in the fuel system, can plug your fuel components. Your lawn mower doesn’t stay running when the fuel line or fuel filter becomes plugged creating a fuel restriction. Read more about why your mower is not getting fuel and how to fix it in this guide for a push mower, riding mower or zero turn mower.

Dirty Carburetor

The carburetor regulates the amount of fuel that is mixed with air to form a combustion in the cylinder. When a carburetor is dirty from old fuel, the small parts that allow it to function can become plugged or stuck. Your lawn mower will not be able to get sufficient fuel. It will begin running sluggish or won’t stay running.

Before you remove the carburetor from the lawn mower, perform these quicks steps to isolate your fuel problem to the carburetor.

  • Confirm you are getting fuel flow to the carburetor and don’t have a fuel restriction elsewhere in the fuel system.
  • Remove the air filter and spray carburetor cleaner into the air intake. Start your mower. If it runs fine and then dies, there is a good chance your carburetor must be cleaned and inspected for any failed parts.

You can find instructions on cleaning your lawn mower carburetor here.

Plugged Air Filter

With all the dirt and grass clippings that get thrown into the air when mowing, the air filter can become plugged. It’s important to regularly check and clean the filter. When your engine isn’t able to get the clean air it requires, it will fail to stay running.

Not only will running a dirty air filter cause running problems, it can cause significant engine damage. Keeping the filter clean and replacing it with a new one when needed is a small investment in time and money towards keeping your mower running at its best.

Replace your air filter annually and clean it several times throughout the mowing season using these steps:

Clean lawn mower paper air filter:

  • Remove the air filter from the housing.
  • Wipe out any dirt remaining in the housing. Be careful to not let any dirt fall into the air intake.
  • Tap your filter against a solid surface. What you are trying to do is knock as much dirt out of the filter that will come loose and fall out.
  • Hold your air filter up to a light source and make sure you can still see light shine through the paper element. If you can, go ahead and reuse your air filter.  If you can’t, it’s time to buy a new one.
  • Reinstall the air filter and attach your air filter housing cover.

Clean lawn mower foam air filter:

  • Remove the air filter from the housing.
  • Wipe out any dirt that is in the filter housing. Don’t allow any dirt to fall into the air intake.
  • Inspect your filter. If you find any dark spots, tears or your filter is dry and brittle, you must replace your filter with a new one. If it appears to be in good condition proceed with cleaning it.
  • Wash your foam filter with water and a mild dish soap. Rinse to remove the soap from the filter.
  • Lay flat to dry. Placing your filter in the sun will help speed up the drying process.
  • Once the filter is completely dry, coat it with a foam air filter oil. You want it completely covered with oil, but you don’t want it to be dripping of oil. If you get too much oil on the filter, ring out the extra oil or use a paper towel to absorb excess oil.
  • Reinstall the air filter and attach your air filter housing cover.

Choke Set in the Wrong Position

If your mower has a choke lever, it might be set in the wrong position. The choke restricts air flow to allow a higher concentration of fuel into the combustion chamber when starting a cold engine. When the choke isn’t adjusted correctly after the mower warms up, the mower will stop running because it isn’t getting sufficient air flow.

Dirty Spark Plug

A dirty or damaged spark plug can cause your mower to run rough or quit running. A dirty spark plug is one that has carbon or oil buildup on the tip. A damaged one is when the porcelain is cracked or the electrodes are burnt.

Check your spark plug and replace if you find any of these conditions. Make sure the plug is gapped to the engine manufacturer’s specification and that the spark plug wires are securely attached. It is best practice to install new spark plugs annually.

Bad Ignition Coil

The ignition coil can be the cause your lawn mower won’t keep running. The windings on the ignition coil can separate and short out when the lawn mower gets hot. This will result in the spark plug not being able to create spark because it is unable to get the voltage it needs. Check for a break in the continuity using an ohm meterOpens in a new tab..

Bad Battery or Charging System

The battery on your lawn mower may be going bad an unable to hold a charge. You may also have a problem with the charging system. Read more about checking your battery and the charging system in this guide.

Bad Fuel Cap

A lawn mower fuel cap has a vent that allows air to pass through the cap. Without this vent, the fuel tank will act like a vacuum and not allow your mower to get fuel. The fuel cap can get plugged which won’t allow air to pass through the cap and therefore causing your mower to stop running.

Once the mower has stopped running, remove the fuel cap and start your mower. If it starts and runs fine, place the cap back on your fuel tank while allowing your mower to continue to run. If your mower shuts off after isn’t been running a while, you may have a bad fuel cap.

You can attempt to clean the cap and unclog the vent, but this doesn’t always work. You may have to buy and install a new cap.

Still Having Problems with Your Lawn Mower

The items listed above are the most common problems you will encounter into when your lawn mower stops running. If you have checked all the items above and still have problems or if you have a different type of problem, check out my guide Common Lawn Mower Problems and Solutions.

If you are running into engine problems or electrical problems, you may want to bring your mower to your local mechanic to troubleshoot. Troubleshooting these issues can get a little in depth for the average owner. I’ve seen owners just throw parts at their mower hoping to find a fix. This can get pretty expensive.

If you’re unsure on the cause and repair for your mower’s problem, it’s time to consult an experienced mechanic.

Powered Equipment Team

We're just a guy and a girl obsessed with outdoor power equipment! We are excited to share the knowledge and tips we have learned over our combined 55 years in the power equipment industry. We have both ran equipment dealerships and took pleasure in helping our customers everyday providing equipment repair, parts, purchasing, and business tips to our residential and commercial clients. We hope our blog will help you with your next purchase, repair, or project.

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