If your lawn mower starts up fine but shuts down within seconds or minutes, you’re not alone. This is a common issue many homeowners face, especially at the start of mowing season. The good news? It’s often caused by a few simple and fixable problems. This article will break down the most common reasons why your mower may start and then stop, how to troubleshoot the issue step by step, what you can do to fix it, and when to call a professional.
Common Causes
Fuel Issues
Fuel is the lifeblood of your lawn mower’s engine. If there’s a problem with the fuel, the engine won’t run properly.
Old or Contaminated Fuel: Fuel left in the tank over the winter can go stale. Ethanol in gasoline attracts moisture, which leads to separation and gum buildup. This can clog up parts and cause the engine to stall.
Empty Fuel Tank: It may sound obvious, but sometimes the tank may have just enough fuel to start the mower and then run out within moments. Double-check your fuel level.
Incorrect Fuel Mixture (for 2-stroke engines): Using straight gasoline instead of a gas-oil mix (or vice versa) can damage the engine or prevent it from running smoothly.
Carburetor Problems
The carburetor is responsible for mixing fuel and air in the right ratio. A dirty or clogged carburetor can disrupt this mix, causing the engine to stop shortly after it starts.
Gummed-Up Jets or Needle Valves: Over time, fuel residues harden and block internal passages in the carburetor.
Dirty Float Bowl: If the float bowl has debris or water, it can restrict fuel delivery.
Spark Plug Issues
The spark plug ignites the air-fuel mixture. A faulty spark plug means poor combustion or none at all.
Dirty or Fouled Plug: A plug covered in carbon deposits or oil can fail to spark.
Worn Electrodes: Over time, the electrodes wear down, reducing the efficiency of the spark.
Air Filter Blockages
Engines need air to burn fuel. A clogged air filter suffocates the engine, causing it to die shortly after starting.
Dust and Grass Buildup: Filters clogged with debris won’t allow enough air to pass.
Wet or Oil-Soaked Filters: Moisture or oil in the filter restricts airflow.
Fuel Cap Vent Blockage
Your mower’s fuel cap has a small vent to equalize pressure inside the tank. If that vent is blocked, a vacuum can form and stop fuel flow.
Symptoms: Engine starts and stops as vacuum builds. If you loosen the cap and it runs better, the vent is likely the issue.
Troubleshooting Steps
Before you tear the mower apart, follow these basic diagnostic steps:
Check the Fuel
Drain the tank and replace it with fresh gasoline (use a fuel stabilizer if storing for later).
Make sure you’re using the correct mixture if it’s a 2-stroke engine.
Inspect the Air Filter
Remove the air filter and see if the engine runs longer without it. If it does, the filter is likely clogged.
Clean or replace the filter if needed.
Examine the Spark Plug
Remove the plug and inspect the tip.
Clean it with a wire brush or replace it if worn or fouled.
Test the Fuel Cap
Loosen the cap slightly and try starting the mower.
If it runs fine, clean or replace the fuel cap.
Check the Carburetor
Remove the bowl and inspect for dirt or water.
Spray carb cleaner through the jets and passages.
If heavily gummed, remove the carburetor and clean it thoroughly or replace it.
Solutions
After identifying the issue, here’s how to solve it effectively:
Cleaning or Replacing Parts
Air Filter: Tap it gently to remove loose debris or wash it if it’s a foam filter. Replace if heavily clogged or damaged.
Spark Plug: Use a wire brush to clean it. If the gap is off or it’s badly fouled, replace it with a new one.
Carburetor: Soak the carburetor in cleaner and use compressed air to clear blockages. If it’s too dirty or corroded, replacement may be cheaper than a full rebuild.
Fuel System Maintenance
Use ethanol-free fuel if possible, or add a stabilizer to avoid moisture buildup.
Drain the tank and run the mower dry before winter storage.
Keep your gas can clean and store fuel no longer than 30 days.
Regular Maintenance Tips
Check and replace air filters every season.
Inspect and clean the spark plug annually.
Clean the underside of the mower deck to prevent clogs.
Run the engine dry at the end of each mowing season to prevent fuel gumming.
Safety Precautions
Working on small engines involves sharp blades and flammable fuel. Always put safety first.
Disconnect the Spark Plug: Always remove the spark plug wire before inspecting or servicing the mower.
Work in a Well-Ventilated Area: Especially when working with fuel or carburetor cleaner.
Wear Gloves and Eye Protection: Prevent injuries from fuel spills or sharp parts.
Let the Engine Cool: Don’t work on a hot engine.
When to Seek Professional Help
If you’ve tried all the above and your mower still starts and stops, it might be time to call a pro.
Internal Engine Issues: Low compression, valve problems, or engine damage may need a technician’s help.
Advanced Carburetor Repairs: Some carburetors are sealed or hard to service without special tools.
Electrical Problems: If there’s an issue with the ignition coil or kill switch wiring, it’s best left to a repair shop.
Conclusion
A lawn mower that starts and then stops can be frustrating, but in most cases, the cause is something simple. Old fuel, a clogged carburetor, or a dirty spark plug are all common culprits. With the right troubleshooting steps and a bit of routine maintenance, you can often fix the problem yourself. Just remember to follow safety guidelines and don’t hesitate to get help if the issue proves stubborn.
By keeping your mower clean, fueled with fresh gas, and well-maintained, you can enjoy a smooth, hassle-free mowing season.
Related topics:
- How to Sharpen Lawn Mower Blades Angle Grinder?
- How to Sharpen John Deere Lawn Mower Blades?
- How to Sharpen a Rotary Lawn Mower?
