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This is Why Your Riding Lawn Mower Won’t Stay Running

You made a significant investment into your riding mower so you want to make sure it stays running at its best. This includes servicing your lawn mower annually and completing some maintenance throughout the season. Even though you do your best to keep your mower in good condition, you can still encounter problems when operating your riding mower.

A riding lawn mower won’t stay running when the fuel is old causing fuel restrictions in the fuel lines, fuel filter and carburetor. It can also quit running when the riding mower has a bad fuel pump, dirty spark plug, faulty ignition coil, or a plugged air filter.

Keep reading for more items that can cause your riding mower to stop running.

Riding mower won't stay running

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

Reasons Your Riding Lawn Mower Won’t Stay Running

Bad or Old Fuel Causes a Riding Mower to Stop Running

Letting fuel sit in your riding mower is not good for the fuel system or engine. Gas should be consumed within 30 days before it begins to breakdown and become less effective. This includes gas that is sitting in a fuel storage container as well.

If you purchased more fuel than you can use within 30 days, add a fuel stabilizer to make your fuel last a little longer without breaking down. I use a product called Sea Foam Motor Treatment because it not only stabilizes the fuel, it also cleans the fuel system and reduces moisture. You can read more about its advantages in this article.

Ethanol, an alternative fuel used in gasolines today, attracts moisture which is corrosive to the fuel system. This ethanol and water mixture leaves behind gummy deposits that stick to fuel components resulting in a restricted fuel flow. This mixture will also separate from gasoline over time and sink to the bottom of the fuel tank. It runs hot through your engine and can cause damage.

Keep these things in mind when selecting gas for your riding mower:

  • Use an unleaded gasoline with a minimum octane rating of 87 and maximum ethanol content of 10%.
  • Avoid fuels with an ethanol content greater than 10% including fuels sold as E15, E30 and E85. These fuels contain up to 15%, 30% and 85% ethanol respectively.
  • Ethanol-free fuel is best, but it is more costly. It can be purchased at some fuel station pumps sold as REC-90 or recreational fuel. You can also find it sold in canisters at the hardware store. This is the more expensive option.
  • Store fuel in a cool dry location away from combustibles and moisture.
  • Add a fuel stabilizer when you are unable to consume it within 30 days.

When you find your fuel is old, use a fuel siphon pump to remove the old gas. Fill the fuel tank with fresh gasoline with a fuel additive like Sea Foam to remove moisture and clean the fuel system.

Plugged Fuel Filter Causes a Riding Mower to Stop Running

The fuel filter can become plugged with dirt and debris when it isn’t changed out regularly. The filter is used to screen the fuel as it comes out of the fuel tank and before it enters the mower’s fuel system. A plugged fuel filter will restrict the amount of fuel that is able to pass through the filter being a reason your riding mower won’t keep running.

A dirty or plugged filter must be replaced. Stop the fuel supply using the fuel shut-off valve or crimp the fuel line using pinch pliers. Remove the fuel filter from the fuel lines. Have a rag available to catch fuel that remains in the fuel line and filter.

Install the new fuel filter with the arrow on the side of the filter facing the direction of the fuel flow. The arrow should be pointed toward the carburetor and away from the fuel tank. Turn your fuel supply back on.

Clogged Fuel Lines Causes a Riding Mower to Stop Running

Gummy deposits from running old fuel can collect in your fuel line causing a fuel restriction. To find a blockage in the fuel line, start and stop the fuel flow by crimping the fuel line or using the fuel shut-off valve. With the fuel flow stopped, remove the end of a section of fuel line and place it in a container.

Start your fuel flow and confirm you are getting good flow coming out of the fuel line. If you are, reattach your fuel line. If you are not getting good flow, with your fuel flow stopped, remove the fuel line from your riding mower.

Spray carburetor cleaner into the line to loosen the clog. Next, blow compressed air through the line to loosen and remove the clog. Repeat as necessary until the clog has been removed. If you are unable to remove the clog or you find the line is dry and cracked, replace the fuel line with a new line of the same length and diameter.

Bad Fuel Pump Causes a Riding Mower to Stop Running

Your riding lawn mower will use a fuel pump when the carburetor sits higher than the fuel tank and needs a pump to move fuel against gravity. A vacuum fuel pump builds pressure off the engine that activates the diaphragm forcing gas to the carburetor.

Confirm the fuel pump is functioning properly by, first, checking to make sure you are receiving fuel flow to the inlet port on the pump. You may have already checked this in the previous step when you checked your fuel lines for blockage. If not, go back to the fuel line section for help.

Once you have confirmed you are getting sufficient fuel to the fuel pump, remove the fuel line from the carburetor and place in a container. Next, start your fuel flow and start your riding mower. You should see a steady or pulsating stream of fuel flowing out of the fuel line signifying your fuel pump is working correctly.

Replace a bad fuel pump that is damaged or is not pumping a stream of fuel out of the pump.

Dirty Carburetor Causes a Riding Mower to Stop Running

The carburetor is an important component on your riding mower. When it doesn’t function correctly your riding mower can stop running. The carburetor regulates the amount of gas that is mixed with air to form a combustion in the cylinder.

A little fuel is stored in the fuel bowl after it leaves the fuel tank. When the fuel gets old it can leave a varnish and sticky deposits that clogs the fuel jet and gums up the small components in the carburetor. A dirty carburetor will cause your riding mower to run sluggish and cause it to die.

A dirty carburetor must be cleaned. 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 instruction in “How to Clean a Riding Mower Carburetor: Step-By-Step“.

Plugged Air Filter Causes a Riding Mower to Stop Running

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 a riding 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.

Incorrect Choke Setting on a Riding Lawn Mower

The choke restricts air flow to allow a higher concentration of fuel into the combustion chamber when starting a cold engine. Once the engine is warm, the choke must be adjusted to allow air to mix with fuel to continue to run.

When the choke lever isn’t adjusted correctly after the mower warms up, the mower will sputter and stop running because it isn’t getting sufficient air flow.

Dirty Spark Plug Causes a Riding Mower to Stop Running

A fouled spark plug can cause your spark plug to fire intermittently causing a riding mower to run sluggish and die. Remove the spark plug and check it for oil, dirt and carbon buildup. You can attempt to clean a dirty spark plug with a wire brush and reuse it. I prefer to replace the plug with a new one since it plays an important role in a good running mower and it is a relatively inexpensive part.

You must also make sure the spark plug is gapped according the the engine manufacturer’s specifications and securely attach the spark plug wire (spark plug boot). These items can also cause your riding mower to stop running.

Bad Ignition Coil Causes a Riding Mower to Stop Running

The ignition coil can be the cause your riding lawn mower won’t stay 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 meter.

Bad Fuel Cap Causes a Riding Mower to Stop Running

The fuel cap on a riding lawn mower is designed to vent to allow air to pass through the cap. Without this vent, the fuel tank will create a vacuum that will prevent fuel from leaving the fuel tank and getting to the engine. A cap with this problem can run for a bit, but eventually shut down and stop running.

Once the mower has stopped running, remove the fuel cap and start your mower. If it starts and runs fine, you may have a problem with the fuel cap vent. Place the cap back on your fuel tank while allowing your mower to continue to run to see if the mower shuts off after a while to further indicate you have a gas cap problem.

You can attempt to clean the cap and unclog the vent, but this doesn’t always work or may work temporarily. I recommend purchasing a new riding mower fuel cap.

Riding Lawn Mower Engine Overheats and Won’t Stay Running

When a riding engine overheats, it will shut down and stop running. This could be due to a low engine oil level, wrong type of oil, clogged mower deck and plugged air filter. For additional reasons a riding mower can overheat, check out my guide Things That Can Cause a Lawn Mower to Overheat.

Still Having Problems With Your Riding Mower?

As a lawn mower owner, when you own it long enough, you are going to run into different types of problems. This may include problems where you riding mower is smoking, cutting uneven, losing power, not starting, leaking fuel and more.

Check out this handy guide including charts for common riding mower problems and solutions:
Common Riding Lawn Mower Problems & Solutions.

If you are unable to fix your riding mower or don’t want to attempt a more complicated repair, have your local lawn mower dealership or repair shop for assistance.