A lawn mower that starts and won’t stay running isn’t getting sufficient air, fuel, and spark. This can be due to old fuel, clogged fuel line, plugged fuel filter, dirty carburetor, plugged air filter, bad spark plug, faulty ignition coil, clogged fuel cap, or an incorrect choke setting.
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.
Other articles that may help you with your mower:
- Reasons your mower starts then dies
- Why your lawn mower is getting hot and overheats
- Adding too much oil to your engine can cause it to stop running
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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.
11 Reasons Your Lawn Mower Won’t Stay Running
1. Bad or Old Fuel
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 mower engine. Read more about the right type of gas to use in your gas-powered lawn mower here.
REPAIR: Drain the old fuel from the tank. Mix a fuel stabilizer like Sea Foam Motor Treatment or STA-BIL to with fresh gas. Add it to the fuel tank.
The fuel stabilizer not only helps clean the fuel system and remove moisture, but it also keeps fuel stable so it last a little longer.
2. Restriction in the Fuel System
Fuel system problems often cause the engine to stall. When moisture evaporates in the fuel system gummy deposits are left behind that can plug your fuel components.
Your lawn mower doesn’t stay running when there is a blockage in the fuel system or faulty carburetor.
3. Clogged Fuel Filter
A fuel filter is used to protect the fuel system and engine from dirt and other contaminates from the fuel tank.
You may have an inline fuel filter inserted between two fuel lines. If you don’t see one of the plastic filters on your mower, chances are your filter is located at the bottom of the fuel tank.
When the filter isn’t replaced regularly or you are running dirty fuel, it can become clogged and not allow fuel to pass through it.
REPAIR: Shut off the fuel supply. Remove the clamps holding the inline filter and then remove the filter. Reinsert the new fuel filter between the fuel lines, install the clamps, and turn on the fuel supply.
If you don’t have an inline fuel filter that is easy to access, you may have a filter at the bottom of the fuel tank. When you aren’t getting good flow through the fuel line and your fuel line isn’t clogged, check this filter.
Do this by emptying the fuel tank first and then replacing the fuel filter.
4. Clogged Mower Fuel Line
Check for a restriction in the fuel line. This can keep a good supply of fuel from getting to the carburetor.
To find a clog in the fuel line follow these steps:
- Shut off the fuel supply by turning the fuel shut-off valve to the off position. If you don’t have a valve, clamp the fuel line to stop the flow.
- Remove the fuel line from the carburetor. (If your mower uses a fuel pump, remove the line from the pump).
- Place the line in a container used to collect fuel. Make sure the container is placed lower than the fuel tank. Fuel will follow gravity and is unable to flow uphill without the use of a fuel pump.
- Start the fuel flow by turning the fuel shut-off valve to the on position or removing the clamp.
- Watch the flow into the container. If you have good flow, move on to checking for other fuel issues.
REPAIR: If you aren’t getting good flow through the fuel line, shut off the fuel supply and remove the section of the fuel line from the mower.
Spray carburetor cleaner into the line to help loosen the clog. Then push compressed air through the line to remove the restriction. Repeat as needed.
Replace a fuel line when you are unable to remove the restriction. You will also want to remove it if it is dry and cracked.
5. 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. A sluggish mower that won’t stay running will often signify a dirty carburetor.
Before you remove the carburetor from the lawn mower, perform these quick steps to isolate your fuel problem with the mower 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.
REPAIR: You can find instructions on cleaning your lawn mower carburetor here. If cleaning doesn’t work, you’ll have to rebuild the carburetor or replace it with a new one.
6. 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, but it can also 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.
REPAIR: 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, or 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 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 foam air filter oil. You want it completely covered with oil, but you don’t want it to be dripping with oil. If you get too much oil on the filter, ring out the extra oil or use a paper towel to absorb the excess oil.
- Reinstall the air filter and attach your air filter housing cover.
7. Choke Set in the Wrong Position
If your mower has a choke lever, it might be set in the wrong position. The choke restricts airflow 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 airflow.
REPAIR: Make sure the choke lever is in the on position to close the choke plate and start a cold engine. It must then be adjusted to the off position for a warm engine.
If the choke is in the right position, make sure the choke plate is opening and closing correcting. You can view the choke plate by removing the air filter.
If the choke plate isn’t moving, use WD-40 to loosen the choke shaft and linkages.
On mowers with an automatic choke, a temperature gauge is used to open and close the choke. If the choke isn’t opening and closing correctly, the choke may be stuck or the temperature gauge placed near the muffler may be faulty.
8. 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.
REPAIR: Check your spark plug and replace it 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.
9. Bad Mower Ignition Coil
The ignition coil (armature) can cause your lawn mower to stop 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 a spark because it is unable to get the voltage it needs.
REPAIR: Check for a break in the continuity using an ohmmeter. Replace a bad ignition coil.
10. Bad Lawn Mower 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 for a while, you may have a bad fuel cap.
REPAIR: You can attempt to clean the gas cap and unclog the vent, but this doesn’t always work. You may have to buy and install a new cap.
11. Overworking the Engine
Your lawn mower may stop running when the engine is overworked. Check these items to make sure you are not overworking the engine or causing overheating problems:
- Clogged cooling system including the engine cooling fins
- Packed mower deck. Dull mower blades make the problem worse.
- Running the mower too fast for the mowing conditions.
- Running the mower with a slow engine speed.
Running Problems FAQ
A lawn mower only runs for a few seconds and then dies due to a dirty carburetor, a wrong choke setting, or bad gas causing fuel restrictions.
A faulty ignition coil, bad gas cap, dirty carburetor, and old gas are the most likely causes of a mower that runs for a few minutes and then dies.
A lawn mower keeps stalling when deposits are left behind by old gas creates fuel restriction in the fuel lines, carburetor, and fuel filter. A clogged air filter, bad ignition coil, bad gas cap, and overworked engine can also cause it to stall.
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 of the cause and repair for your mower’s problem, it’s time to consult an experienced mechanic.