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What If Lawn Mower Starts, Then Dies? Why Won’t My Lawn Mower Stay Running?

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What happens if your lawn mower starts, then dies? Well, lawnmowers are notoriously unreliable. But the grass keeps growing – even if your lawn mower won’t stay running. Ouch! And when you need to cut the lawn, the last thing you want is engine problems with your mower.

Luckily – most gasoline lawnmowers, ride-on or push-type models, have relatively rudimentary engines. Their engines use carburetors and simple electronics that most mechanically minded DIY enthusiasts can service.

So – if your lawn mower won’t stay running, here is the best place to start.

We’ve compiled a set of common lawn mower pain points and how to troubleshoot them. We bet they keep your mower running.

Trying to start the lawnmower after it suddenly quit working.

Ready?

Then hop on board!

Why Won’t My Lawn Mower Stay Running?

A lawn mower starts and then stops running after a few minutes due to three likely causes:

  • The engine is losing spark due to a faulty ignition switch preventing current from powering the ignition coil.
  • Dirt or gum particles in the carburetor are intermittently blocking the fuel jets.
  • Your lawnmower might be overheating.

When your lawn mower starts and then dies immediately, the best place to begin your diagnosis is the mower’s electrical system: 

  • Check the ignition switch. If the lawn mower starts and then cuts out when you turn the key from the start to the run position, it’s a bulletproof sign that your ignition switch is faulty.
  • Safety switches on ride-on mowers, including the seat safety switch and deck-engage safety switch, fail! So, be sure to check these.
  • Check all electrical wiring from the battery to the spark plug for any signs of perishing.
  • Exposed wires may be shorting out the circuit.

Another possible reason why your lawn mower cuts out after you start it is a blocked carburetor. 

  • Fuel standing for more than six weeks begins to oxidize and form gummy globs.
  • Lawnmowers that haven’t been used for months (during winter mostly) will invariably have gummy fuel in the carburetor bowl.  
  • Fuel contaminants can breach the fuel filter and block the carburetor jets.
  • The carburetor jets (the main jet and a pilot jet) supply fuel to the mower engine through tiny holes. The particulate matter floating about in the carburetor bowl can get lodged in the jet holes, as can fuel gum, effectively blocking gasoline flow and starving the engine of fuel.
lawn mower cutting fresh and thick green grass in backyard
We’ve spent entire seasons troubleshooting lawnmowers that start and then die! The usual suspect is a clogged carburetor. However, a dirty carburetor isn’t the only common issue! Check for a dirty spark plug, old fuel or engine oil, or a dirty air filter. But before you troubleshoot anything or take your machine to a lawn mower repair shop, check the gas tank! We also have a few tips to help troubleshoot your carburetor when the mower engine stalls. Here goes!

The Fix: Conduct a lawn mower carburetor service:

  1. Remove the air filter and carburetor from the lawn mower.
  2. Disassemble the carburetor. 
  3. Clean the body and jets of the carburetor with an aerosol carburetor cleaner.
  4. Immerse the disassembled carburetor parts in an ultrasonic cleaner or soak them in a tub of carb cleaner for 12 hours for deep cleaning (do not soak rubber carburetor seals in the carb cleaner).
  5. Dry the carburetor parts with compressed air.
  6. Inspect the jet ports to ensure they are clear of blockages by holding them up to the sunlight.
  7. Reassemble the carburetor and refit it to the lawn mower.
  8. Replace the air filter and refit it to the clean carburetor.
  9. Replace the fuel filter.
  10. Start the lawn mower and let it warm up. 
  11. Adjust the idle mixture screw until you find the highest idling revs position. (A better idle setting will make cold starting less fussy.)

Consult your lawn mower owner’s manual for parts replacement and servicing guidance.

Why Does My Lawn Mower Keep Shutting Off?

When a lawn mower engine cuts out intermittently, the problem is usually an exposed earth wire running from the ignition switch to the ignition coil. When the naked wire touches the mower body, it acts as a kill switch and cuts the voltage from the ignition switch to the ignition coil. 

Other possible causes of intermittent engine shutdown include:

  1. A blocked fuel filter starves the engine of fuel. To fix the problem, replace the fuel filter.
  2. An intermittently blocked carburetor starving the engine of gas will quickly shut your mower down. Clean the carburetor as described below.
  3. Faulty seat and deck safety switches can cause erratic lawn mower shutdowns. To fix, test the safety switches manually for intermittent failure and test for voltage using a multimeter.  
  4. Exposed wiring. Reinsulate bare wire with electrical tape.

Can a Bad Spark Plug Cause a Mower to Stall?

Yes. A bad spark plug can cause a lawn mower to stall if the spark plug dies. However, a stalled mower engine isn’t a typical symptom of a bad spark plug. A bad spark plug will more likely make starting the mower engine difficult due to the gradual deterioration of the electrodes through wear and fouling.

starting the lawn mower after the winter season
Has your walk-behind mower been sitting in your shed all winter? Maybe you’re finally dusting it off for the mowing seasons? Then double-check your fuel and oil level! Condensation can collect inside your mower’s tank during winter. This condensation creates a subpar mixture and fuel quality, which might cause your mower to stall unexpectedly. Replacing the old wintry gas with fresh gasoline can help in this case! (And some new gasoline might save you the frustration of flipping through repair guides or asking your local mechanic for a costly repair clinic.)

How Do You Fix a Briggs and Stratton Lawn Mower Engine that Starts and Dies?

Determine whether the Briggs and Stratton engine starts and dies suddenly due to an electrical problem or a carburetor issue. 

Electrical faults are the most common reason a Briggs and Stratton lawn mower’s engine stops suddenly. These electrical faults include the following.

  • The ignition coil may run until it gets warm and then stops working. 
  • The ignition switch is faulty. Repair or replace the ignition switch if the engine cuts out when you turn the key back to the start position.
  • The seat and deck engage safety switches are faulty or not making solid contact with the wiring system. Check the connections and the switch’s integrity.
  • Exposed wiring from the safety switches will short-circuit the kill switch, shutting down the engine. Insulate naked wires.

A blocked carburetor will stop the engine. Follow the carburetor service guide above.  

What Would Cause a Lawn Mower to Start and Not Stay Running? 

The most common cause of a lawn mower stopping suddenly after running for several minutes is a fault in the kill wire circuit. 

The solution is to remove the kill wire. And then start the engine. (The kill wire runs from the coil to the ignition switch.) The problem lies in the kill wire circuit if your mower runs without cutting out. The wiring circuit includes the ignition switch, the seat safety switch, and the deck engage safety switch.

  • Check the kill wire circuit for exposed wire and insulate the wiring with electrical tape. (Usually a black wire.)
  • This random, intermittent engine failure may also be due to a partially blocked carburetor. Clean the carburetor as outlined below. 
replacing air filter on gas lawn mower for routine maintenance
Whenever our friends ask why their lawn mower won’t keep running, we tell them to double-check the air filter. Most popular mower engines use foam or paper air filters to collect debris, soot, and gunk that can easily clog your mower’s engine. If these filters get too overburdened with crud, it can easily cause your mower to stall. It’s true – we’ve seen mowers overheat due to a lack of airflow! Check your mower’s user manual for the location and best practices for changing your air filter. However, we usually change (or at least check) ours after every 20 hours of use. No matter what the manual says!

How Do I Clean a Clogged Lawn Mower Carburetor?

The best way to clean a clogged lawnmower carburetor is to remove it from the mower, strip it down in a clean workspace, and blast it with aerosol carburetor cleaner. The carburetor jet holes can get probed with fishing lines to remove particulate matter.

  • Soak the carburetor parts in carb cleaner for 12 hours for a deep clean.

Warning: Do not attempt to clean the jet orifices with metal objects.

holding isolated lawn mower carburetor in hand
Here you see an old carburetor. Carburetors help internal combustion by mixing air with fuel. But the engine fuel can begin evaporating if you let old gasoline stagnate in your mower engine. That evaporation can leave a nasty (and sticky) residue over internal engine components – including your carburetor ports. When the carburetor gets too gunked up (no matter the cause), it can lead to your mower engine stalling or outright stopping after running. If you suspect your carburetor is dirty, remove it and clean it with a towel and aerosolized spray. (We also advise you to wear safety glasses when maintaining your mower. For your peace of mind. And ours! We don’t want our readers to get hurt. Never forget that each year 9,000 children get injured by powered lawnmowers. Stay safe!)

How Do You Clean a Carburetor on a Lawn Mower Without Removing It?

The best way to clean a carburetor is to remove it for a thorough purging of contaminants. However, although not a sure-fire fix, you can clean a carburetor on a lawn mower without removing it by doing the following:

  1. Remove the bowl from the carburetor and allow the fuel to drain out into a safe container.
  2. Disconnect the fuel hose from the fuel tank.
  3. Replace the carburetor bowl.
  4. Fill the carburetor with carburetor cleaner via the fuel hose. 
  5. Reconnect the fuel hose to the fuel tank.
  6. Allow the carburetor cleaner in the carb to stand for 48 hours to dissolve contaminants and clean the carb.
  7. Remove the bowl and drain the carburetor cleaner into a safe container.
  8. Flush the opened carb with a few ounces of gasoline.
  9. Replace the carburetor bowl.
  10. Start the engine. 

Read More!

How Do I know if My Lawn Mower Carburetor is Bad?

The first sign of a failing carburetor is your lawn mower engine will start to run rough. If the lawn mower runs smoothly with the choke on but not with the choke off, the carburetor needs attention. 

When the choke is engaged, the idle mixture runs rich, giving the engine more fuel than air. 

The choke gets used to assist when cold-starting the engine. The carburetor needs servicing if the choke keeps a hot engine running smoothly.

  • To fix a faulty carburetor, follow our carburetor-cleaning guide.
holding a spark plug from gas powered lawn mower
Spark plugs help manage your mower’s fuel combustion. Your lawnmower engine can’t start – or run properly without them! So check your spark plug wires if your lawnmower starts and dies. Or if it won’t stay running! An old spark plug with thick, black residue needs to get replaced. At the very least, scrub your spark plug with a wire brush. (We usually double-check our spark plug every 50 hours of lawn mower use. Double-check your lawn mower’s user manual for guidance on how to change yours.)

Why Does My Lawn Mower Run for Ten Minutes Then Dies?

If your lawn mower starts then dies after ten minutes, it’s usually due to a faulty ignition coil. As aging ignition coils heat, they become less capable of generating sufficient voltage to trigger the spark plug, which results in the engine dying. 

Another cause of engine stoppage after several minutes of operation is an exposed kill circuit wire touching the mower body and short-circuiting the ignition system.

What Is the Easiest Way to Troubleshoot a Lawn Mower Engine?

The easiest and cheapest way to troubleshoot a lawn mower engine is to start with the spark plugs. Ensure the electrodes are carbon-free, flat-surfaced, and set to the correct gap. Then change the fuel and air filters before removing the carburetor for servicing.

Conclusion – All Cut and Dried

Why outsource your lawn mower repairs and servicing when you can save time and money doing it yourself? Having the skills and tools to troubleshoot your lawn mower saves you summertime anguish.

We trust this troubleshooting guide will help your lawn mower self-sufficiency and repair proficiency. Dramatically!

Good luck on that lawn!

We invite you to ask if you have struggled with your lawn mower – especially if your lawn mower starts and then dies. Or, if you have tips about keeping your lawn mower running without stopping? We invite you to share!

Thanks again for reading.

And have a great day!

What If Lawn Mower Starts and Then Dies? References, Sources, and Works Cited:

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