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Your Lawn Mower Starts & Then Dies: Fixed

Over the years I have been asked by many homeowners and professional lawn care staff about why their mowers always seem to start up and then they die. Most of the time, this problem is an easy fix so you don’t have to continue to fight with this problem

The most common reasons your lawn mower may start then die are bad gasoline; a dirty carburetor that is unable to regulate the mixture of air and fuel; too much oil is in the crankcase; a plugged air filter restricting air flow; and a broken fuel cap that is unable to vent.

Whether we are working with single cylinder or twin cylinder engine, it seems like they all happen to present the same start up and dying problem at some point in the life of the lawn mower. When this problem happens to you, it may seem natural and easy to just run out to your nearest lawn mower parts store and buy a new spark plug. That’s not the first place I would start.

If your mower starts, you know you’re getting spark so replacing the spark plugs may not fix anything. Read on to find the most common reasons your lawn mower dies and how to fix it. This will also address what to do when your push mower starts but won’t stay running or your riding mower starts then dies.

fix a lawn mower that starts and then dies

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Follow all safety instructions provided in your equipment operator’s 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.

7 Reasons Why Your Mower Starts Then Dies

1. Bad Fuel in Lawn Mower

Bad Fuel in your lawn mower can cause your mower to die after running. Gasoline usually only lasts 30 days and then it starts to break down and fail. It loses its ability to run good and hot because chemicals added to fuel today start to decay or fall apart.

Most gasolines available today have ethanol in its makeup. Fuels treated with ethanol tend to collect moisture from the air. The water can evaporate leaving a residue in the fuel tank that can clog the fuel system. If your fuel is over 30 days old, drain the fuel tank, flush the tank, and fill with fresh fuel.

  • Fuel Stabilizer Additive
    You may want to consider adding a fuel stabilizer to your fuel. Mix the stabilizer with the fuel in a fuel can before adding it to your lawn mower’s gas tank. This will prevent the new fuel from breaking down quickly.

    I like using a product called Sea Foam because it has cleaning agents in it for the engine. Not only is it better for the carburetor, but also for the valve train as well. It helps keep the carbon down on top of the piston when it is in use. Read more about Sea Foam in our article “Why Use Sea Foam Fuel Additive in a Lawn Mower“.
  • Recreational Fuel or Non-Ethanol 4-Cycle Fuel
    You can find recreational fuel at many gas stations. This fuel does cost more, but it does not contain ethanol. Big box stores and small engine retail stores offer cans of non-ethanol 4-cycle fuel.

It’s important to treat fuel obtained from a gas station when fueling from a pump. You never know how old the fuel is. I recommend buying fuel from a busy gas station. There is no need to treat recreation fuel, but it will not hurt it if you do. For a more in depth article about the correct fuel for your lawn mower read, “This is the Type of Gas Lawn Mowers Use“.

2. Lawn Mower Carburetor is Dirty

A dirty lawn mower carburetor can be the cause of your lawn mower not running. The carburetor is designed to regulate the amount of air with the right amount of fuel to create a combustion. You will need to check for buildup of deposits left behind by bad fuel and clean your carburetor if necessary. This may sound complicated, but it really is not.

If you are not very mechanically inclined, you should bring your mower into a repair center, but if you are mechanically inclined then read on. Note: if your carburetor is in a condition that is beyond cleaning, you will need to replace it.

How to Clean Your Dirty Carburetor

  • Spray carb cleaner in the air intake: 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 we need to get inside the carburetor.
  • Gather tools needed: You will need pliers, a screwdriver, sockets and ratchets so you to take your carburetor apart without destroying parts.
  • Take a photo for reassembly. With all of the small parts in a carburetor, it is a very good idea to take several pictures while you are tearing down the carburetor so you can refer to them when rebuilding.
  • Remove throttle cable and choke cable if your mower has one.
  • Undo the filter housing: Remove the filter housing and remove the screws and nuts attaching the carburetor.
  • Slowly remove the springs: When removing the spring, be careful to not stretch out the springs. You may have to twist the carb a bit to get the springs off. There is a gasket located between the engine block and the carburetor you need to make sure you don’t tear it.
  • Remove the bottom screw from the float bowl. The float bowl is located on the bottom of the carburetor. This is where gasoline is stored inside the carburetor. Have a rag ready to catch any gas remaining in the bowl.

    When you remove the bowl, you need to be careful not to damage the o-ring around it. This is the o-ring that looks like a rubber band. DO NOT get any carb cleaner or other substance on the o-ring as it will stretch out and you won’t be able to reuse it.
  • Check 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.

    Using a flashlight for assistance to locate the holes, take a thick wire to clean them out. Use carb cleaner to rinse out the unclogged holes.
  • Check 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.
  • 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.
  • Add new fuel supply that contains and fuel stabilizer before you start your mower. Pour the fuel mixture into the gas 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.

3. Too Much Oil in the Crankcase

When there is too much engine oil in your lawn mower, your engine may smoke. It may run terribly and eventually shut down. Too much oil may create a smoke causing your air filter to plug up if the engine oil can’t pull clean air.

As a result, the engine may pull air and oil from the crankcase causing the air filter to become plugged. The lack of air can cause the mower to shut down.

For more details on the damage of overfilling your engine crankcase with oil read “This is What Happens If You Put Too Much Oil In Your Lawn Mower

4. Plugged Air Filter

I’ve had customers bring in their lawn mowers for repair because they can’t keep them running. They tell me they have checked everything and their last resort is taking it to a mechanic to be fixed. Many times, their issue was just a plugged air filter that the owner could have easily changed.

Routine air filter change

You should be performing regular maintenance checks on your lawn mower to keep it running at its best. Checking the air filter is one item that needs to be inspected regularly. You can find air filter cleaning procedures here.

5. Bad or Dirty Spark Plug

A dirty spark plug can foul out causing your engine to stop running. It may have produced enough spark to start your mower, but it may be unable to keep it running. Remove your spark plug and check the condition.

Look for signs of carbon buildup or cracked porcelain. You can attempt to clean your spark plug to remove dirt and reuse. A damaged or excessively dirty dark spark plug must be replaced.

When the spark plug wire(s) is loose or the gap is not correct, it may cause intermittent running or starting problems. Make sure your spark plug has the correct gap and the wires are the spark plug wires are securely attached.

6. Choke is in the Wrong Position

Many lawn mowers utilize a choke. A choke is used to restrict airflow to allow more fuel into the combustion chamber while the engine heats up. A lawn mower uses the choke to start a cold engine. When the choke is left on after your mower starts, your engine receives more fuel and less air than it requires causing it to shut down.

7. Broken Lawn Mower Fuel Cap

Fuel caps are designed to be vented. If the vent is clogged or the cap is broke your engine may die because it cannot get fuel. If your cap won’t vent, a vacuum is formed in the tank which then doesn’t provide fuel. Loosen your cap and start your mower to check to see if your cap may be broke. Replace with a new cap if you are able to start your lawn mower with the cap loosened allowing it to vent.

In Summary

Your lawn mower starts but won’t stay running because of a fuel restriction, too much oil in the crankcase, a plugged air filter, a dirty spark plug, a clogged carburetor or your mower is running too rich. If you have checked all of these items and are still having problems with your mower starting then shutting down, it’s time to bring your mower to a lawn mower repair shop.

My top items to keep on hand to service & troubleshoot your lawn mower

Socket & Allen Wrench Set – Tool set needed to service & troubleshoot your mower problemsCarburetor Cleaner – Clean clogs & buildup in fuel system
Multimeter – To check voltage, continuity & current to identify electrical problemsFuel Stabilizer – Stabilize & clean your fuel to minimize fuel system buildup
12-Volt Battery Charger – Battery/trickle charger to start your mower & slowly charge your batteryFilter Wrench – Helps loosen your filter
Oil Drain Pan – To collect oil with spout to place in containers for disposalBattery Powered Inflator – Keep your lawn mower tires inflated to prevent uneven cutting or steering issues

Still Having Problems with Your Lawn Mower?

Lawn mower ownership doesn’t not come without its frustrations. Own a lawn mower long enough, you are bound to run into many lawn mower problems including starting, smoking, leaking, cutting and overheating.

For a list of the most common lawn mower problems and items that can cause them, check out my guide “Common Lawn Mower Problems: Solved!