Lawn Mower Runs For Awhile Then Dies

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Working with a lawn mower that shuts down after a while of use can be very frustrating and prevent you from getting much work done. There are various reasons why this might occur.

In this article, I talk about some of the common reasons why your lawn mower dies after running for a while and practical troubleshooting tips to help you diagnose and fix the problem.

Reasons Why Your Lawn Mower Runs For AWhile Then Dies

The reasons your lawn mower dies after running for awhile might include:

  • Dirty/clogged carburetor
  • Clogged fuel cap vent
  • Dirty air filter 
  • Stale gas
  • Insufficient oil/too much oil
  • Bad spark plug
  • Bad ignition coil
  • Dull blades

Tools You Need For This Job

Some tools you may need for this job include:

  • Work gloves
  • Screwdriver
  • Spark tester
  • Wire brush
  • Siphon
  • Clean rag
  • Blade sharpener

Lawn Mower Runs For AWhile Then Dies: Causes, Diagnosis, and Fixes

1.  Dirty/Clogged Carburetor

The primary cause of your lawn mower shutting down after running for a while is blocked fuel pathways as a result of a dirty carburetor. 

Your lawn mower may develop a clogged carburetor if fuel is left in it for more than 30 days. Over time, some of the fuel’s components evaporate, leaving behind a thick and sticky residue.

Additionally, with time, debris and dust may find their way into the carburetor bowl and clog the pathways. 

This buildup of dirt and fuel residue impairs engine performance by clogging fuel and carburetor passageways and can cause the engine to die after running for a while.

Diagnosis:

Take out the carburetor and check for dirt/ debris in its jets and bowl. If the fuel in the carburetor bowl is sticky and thick, it may be clogging the carburetor.

Fix:

Use a carburetor cleaner to clean and unclog it.

2. Clogged Fuel Cap Vent

The fuel cap vent can cause the engine to die after running for a while if it gets clogged. As fuel is consumed by the engine, the tank’s fuel level falls. 

Most lawn mowers have a little air vent lid on the fuel tank that allows air to enter the tank to avoid a vacuum from building. 

A vapor lock develops when the vent on the fuel cap is clogged, preventing air from entering the tank. 

This causes the engine to stall and halts the flow of fuel to the carburetor. As a result, the engine shuts down after a short period due to a lack of fuel entering the carburetor.

Diagnosis:

  • Open the fuel cap slowly. If the cap vent is clogged, you will hear the sound of air getting sucked into the tank as a result of the vapor lock.
  • Also, loosen the cap a little bit and run the engine. If it runs fine, then the cap vent is blocked 

Fix:

  • Clean the fuel cap and unclog the vent
  • Replace the cap if the vent is severely damaged

3. Dirty Air Filter

Insufficient air getting into the engine can throw off the fuel and air ratio and cause your lawn mower to overheat and die after a while. 

Your lawn mower may die after a while due to several factors, including trapped air and engine overheating brought about by a clogged air filter.

More air is required by the engine as it gets hotter. To avoid overheating and malfunction, the engine needs cool air inflow from the air filter as it warms up. 

When the air filter gets dirty, it blocks air from entering the engine, resulting in overheating and eventual shut-down.

Diagnosis:

Remove the air filter housing and inspect the air filter. If it is covered with too much dirt and oil, it is clogged.

Fix:

Wash or replace the air filter.

4. Bad/Stale Gas

Stale or outdated fuel in the carburetor bowl may also be the reason your lawn mower runs for awhile and dies. 

After 30 days, fuel will become stale and leave behind a sticky residue that may interfere with the carburetor’s fuel delivery.

The carburetor rusts from stale fuel, which also clogs fuel lines and carburetor jets. As a result, the fuel supply drops, and the engine stalls.

Diagnosis:

The fuel tank should be drained, and the engine should be poured into an empty container. 

If there is a slimy or sticky residue in the fuel, the fuel is likely old and has clogged the carburetor.

Fix:

  • Empty the fuel tank and carburetor bowl of stale fuel
  • Clean the carburetor bowl with carb cleaner
  • Refill the fuel tank with new fuel

5. Insufficient or stale engine oil

The purpose of engine oil is to lubricate and cool the moving components. The moving parts in your lawn mower’s engine lack lubrication when there isn’t enough oil available, and they will eventually stop working and shut down.

Another potential culprit is stale engine oil. Fresh oil has a golden/amber color. The oil darkens and gets thinner with time as a result of friction, strain, heat from the engine, and other factors.

The moving engine parts can no longer be effectively coated and lubricated with dark, stale engine oil, which causes excessive friction and overheating. 

Your lawn mower may shut off after only a brief period of operation due to this friction and overheating.

Diagnosis:

Check the oil level and state of the oil.

  • If the oil is dark and thin, it is stale.
  • If the oil level is below the Add mark, it is insufficient.

Fix:

Top up or replace the engine oil.

6. Worn out Spark Plug

Another potential cause of your engine stalling after a while is a bad spark plug. The spark plug should be checked next if the oil, air filter, carburetor, and cap vent are okay.

If the spark plug isn’t producing a strong enough spark, your mower will shut down as it runs and becomes hot. 

Spark plugs get worn out over time as a result of heat. The porcelain on the spark plug gets damaged, rendering it useless and unable to generate the sparks the engine requires.

The malfunctioning spark plug won’t be able to produce enough spark when the engine is hot enough to ignite the fuel-air mixture, which will cause the engine to die after a while.

Diagnosis:

Remove the spark plug. If it is dark, very dry, or stained with oil, it is worn out.

Fix:

You can clean the spark plug with a wire brush if the damage is minimal but it is best to replace the spark plug.

7. Bad Ignition Coil

If the issue still occurs after replacing the spark plug, the problem might be from the ignition coil, also referred to as the starter coil. 

The ignition coil is a crucial component of the engine in a lawn mower. It is in charge of sending electricity from the battery to the spark plug, which ignites the mower with a spark.

When an ignition coil is malfunctioning, it will function normally when it is cool but will stop supplying voltage to the spark plug as soon as it gets hot, killing the engine. If your mower dies after awhile, there is a good chance that the ignition coil is broken.

Diagnosis:

Test the ignition coil with a spark tester. If there is no spark, the ignition coil is damaged.

Fix:

Replace the ignition coil.

8. Dull Blades/Clogged Deck

Dull mower blades can overwork the engine and cause it to die after a while. If the blades of your mower are dull or bent, it can make the mower overheat and shut down eventually.

Also, when the deck of your lawn mower becomes clogged with grass, the mower will be incapable of cutting more grass and the blades will be unable to move properly, causing the engine to die after a while.

Diagnosis:

Visually inspect the blades and deck to see if the blades are blunt and if the deck is clogged with grass.

Fix:

  • Sharpen the blades with a blade sharpener if they appear blunt/dull
  • If the deck is clogged, remove all the grass and spray down the bottom of the mower with water to remove any residual debris.

Conclusion

The reason why your lawn mower runs and dies after a while might be due to: a clogged carburetor, clogged fuel cap vent, faulty spark plug, stale oil, bad ignition coil, dirty air filter, or dull blades.

Take some time to inspect the various parts and apply the recommended fixes stated in this article to stop your engine from shutting down after running for a while.