You’ve just finished filling up the gas tank, ready to mow your lawn, but when you pull the cord, your lawn mower starts then dies almost immediately. Frustrating, right? It’s a problem many homeowners have dealt with at one point or another.
The good news is that it’s usually something simple that you can fix yourself. From dirty carburetors to clogged fuel lines, there are several reasons why your lawn mower starts and then dies. Read on as we walk you through the most common causes of this issue and give you easy, step-by-step solutions to get your mower running smoothly again.
Common Causes and Solutions of “Lawn Mower Starts Then Dies”
A lawn mower that starts then dies can be a real headache, but luckily, many of the reasons behind this issue are simple to diagnose and fix. Here are the most common causes and how to fix them:
Dirty Carburetor
The carburetor plays a critical role in mixing air and fuel in the proper ratio to power your lawn mower’s engine. Over time, dirt, old fuel, or even moisture can clog the carburetor, restricting the flow of fuel and causing the engine to start but then die shortly afterward.
This is especially common if the mower has been sitting unused for a while. If you’re wondering why my lawn mower starts and then slowly dies, a dirty carburetor might be the culprit.
How to Fix It:
- Turn off the mower and disconnect the spark plug to prevent accidental starting while you’re working on it.
- Locate the carburetor. Depending on your mower model, this may be near the engine or underneath the air filter. You may need to remove the air filter or plastic covers with a screwdriver to get to it.
- Inspect the carburetor for dirt and debris. If you see gunk, use a carburetor cleaner (available at most auto parts stores) to spray it down. Make sure to remove any visible grime.
- Drain the carburetor bowl. There’s typically a small screw on the bottom of the carburetor bowl that allows you to drain old fuel. Place a container underneath to catch the fuel as it drains.
- Clean the carburetor. If the carburetor is very dirty, you can remove it and soak it in carburetor cleaner or use a cleaning brush to scrub away any dirt or build-up. Pay attention to the small jets and ports that fuel flows through.
- Reassemble the carburetor. After cleaning, reattach it and reconnect any parts you had to remove (air filter, covers). Reconnect the spark plug wire and try starting the mower to see if it runs smoothly.
Old or Stale Gasoline
If you’re asking, why does my lawn mower start then die, old gasoline is another common culprit. Gasoline that’s been sitting in the mower’s tank for too long can degrade, forming varnish and other harmful deposits that can clog the fuel system and prevent proper combustion. Ideally, gasoline should be used within a month or two, as it can begin to break down after 30 days.
How to Fix It:
- Drain the old fuel from the fuel tank. Use a siphon pump or, if you’re comfortable, tilt the mower carefully to empty the tank into a gas-safe container. Be sure to dispose of old gasoline properly (never pour it down a drain or into the ground).
- Inspect the fuel filter. If your mower has a fuel filter, it may be clogged with old fuel or sediment. Remove and inspect it and replace it if it looks dirty or damaged.
- Fill the tank with fresh gasoline. Always use fresh, high-quality fuel. Ideally, use 87-octane unleaded gasoline, but check your mower’s manual for specific fuel requirements.
- Add fuel stabilizer if you don’t plan on using the mower for a while. This helps preserve the fuel and keep it from degrading.
Faulty Spark Plug
The spark plug is responsible for igniting the air-fuel mixture in the engine. Over time, spark plugs can wear out, get dirty, or become covered with carbon deposits, which can result in weak or intermittent sparking. This could be why your lawn mower starts but dies immediately.
How to Fix It:
- Locate and remove the spark plug. Use a spark plug wrench to unscrew and remove the plug. If the spark plug looks worn or damaged, it will need to be replaced.
- Inspect the spark plug. Look for signs of carbon build-up, oil deposits, or physical damage (cracks or corrosion). A dirty plug can often be cleaned, but if it’s severely damaged, you should replace it.
- Clean the spark plug. If the plug looks dirty, clean it using a wire brush or sandpaper. Make sure the electrode is free of carbon build-up.
- Check the gap. Use a feeler gauge to measure the gap between the spark plug electrodes. The gap should match the manufacturer’s recommended specifications, typically found in the mower’s user manual.
- Reinstall the spark plug. Once it’s cleaned or replaced, screw the spark plug back into place and reconnect the spark plug wire. Start the mower to see if it runs more smoothly.
Blocked Fuel Cap Vent
If the vent in your mower’s fuel cap becomes clogged or blocked, it can create a vacuum inside the fuel tank. This vacuum prevents the proper flow of fuel to the engine, causing the mower to start but then stall after a few minutes. This is often overlooked, but it’s a simple fix.
How to Fix It:
- Remove the fuel cap and check the vent hole for any visible dirt, debris, or blockages. The vent hole is typically a small hole located on the underside or side of the fuel cap.
- Clear the vent hole. Use a small pin, needle, or compressed air to carefully clear any debris from the vent. Be gentle, as you don’t want to damage the cap.
- Inspect the cap for damage. Check the rubber gasket around the cap for cracks or wear. A damaged gasket may need to be replaced to ensure a tight seal.
- Reattach the fuel cap and reconnect the spark plug wire. Try starting the mower to see if the issue is resolved.
Dirty Air Filter
The air filter is responsible for keeping dirt, debris, and other contaminants out of the engine, ensuring that only clean air enters the combustion chamber. When the air filter gets clogged with dirt or grass clippings, it can restrict airflow, which might explain why your lawn mower starts and then dies.
How to Fix It:
- Locate the air filter. Depending on your mower model, the air filter is usually inside a plastic housing on the side or top of the engine. Remove the screws or clips to open the housing and expose the filter.
- Inspect the air filter. If it’s visibly clogged with dirt, grass, or other debris, it will need to be cleaned or replaced.
- If the filter is foam or sponge-style, rinse it under water with mild soap, or use compressed air to blow out dirt. Allow it to dry completely before reinstalling.
- If the filter is paper-based, gently tap it to remove loose dirt, but if it’s too clogged or damaged, it’s best to replace it with a new one.
- Reassemble the air filter housing and make sure the filter is seated correctly.Reconnect the spark plug wire and test the mower.
Clogged Blades
Over time, grass clippings, dirt, and other debris can build up around the mower blades, causing them to become clogged or dull. This can strain the engine, reduce cutting performance, and even cause the mower to stall. If your lawn mower died while mowing and won’t start, this might be the issue.
How to Fix It:
- Turn off the mower and disconnect the spark plug wire for safety.
- Raise the mower deck to a higher position so you can access the underside of the mower.
- Inspect the mower blades. Look for any built-up grass, dirt, or debris on the blades and surrounding areas. Use a brush or scraper to remove the build-up. Be sure to wear gloves to protect your hands from sharp edges.
- Sharpen the blades. If the blades are dull or nicked, use a sharpening stone or metal file to sharpen the edges. Alternatively, you can use a blade sharpening kit or take them to a professional for sharpening.
- Reassemble the mower and reconnect the spark plug wire. Test the mower by starting it and mowing a small area.
Moisture or Blockage in the Fuel Line
Over time, water or dirt can enter the fuel system, causing blockages or disruptions in fuel flow. When the mower starts, but fuel can’t flow properly due to a blockage or contamination, the engine will run for a short while and then die as it runs out of fuel.
How to Fix It:
- Inspect the fuel line. Locate the fuel line running from the tank to the carburetor. Check for any visible cracks, leaks, or signs of debris or moisture.
- Check the fuel filter (if your mower has one). A clogged or dirty fuel filter can also cause the engine to stall. Replace it if it looks clogged or worn.
- Clear the fuel line. Use compressed air or a small flexible brush to clear any debris from the fuel line. If the fuel line appears cracked or damaged, it should be replaced. If moisture is present, drain the fuel line and tank before refilling with fresh fuel.
- Reassemble and try starting the mower again to see if it runs smoothly.
When to Replace a New Lawn Mower
Sometimes, even with regular maintenance, your mower may keep failing, leaving you wondering if it’s time for a new one. If you’ve tried fixing these issues but they keep recurring, it might be more cost-effective to invest in a replacement.
- Frequent Repairs: If you’re constantly replacing parts like spark plugs, carburetors, or air filters, the cost of repairs can quickly add up. A new mower might save you money in the long run.
- Excessive Engine Wear: An engine that struggles to start, stalls frequently, or emits unusual noises may be reaching the end of its lifespan.
- Old Age: Lawn mowers typically last 5–8 years with proper maintenance. If your mower is older and breaking down more often, consider upgrading to a more efficient model.
- Severe Rust or Damage: If the mower deck, frame, or engine has significant rust, cracks, or corrosion, this can affect safety and performance, making repairs costly or ineffective.
- Outdated Technology: Newer mowers often feature improved fuel efficiency, better safety features, and easier-to-use designs. If your mower is outdated and lacks essential features, upgrading could be a better long-term investment.
Conclusion
A lawn mower starts then dies can be a real inconvenience, but don’t worry—most of the time, the problem is easy to fix. Whether it’s something as simple as a dirty air filter or stale gas, taking care of these small issues can get your mower back in action. Of course, if you’ve tried everything and it still won’t start, it might be time to think about replacing it. But with a little maintenance and some attention to detail, your mower can keep running strong season after season.
FAQs
Why does my lawn mower only run for a few seconds then dies?
If your lawn mower runs for a few seconds and then dies, it could be due to old or contaminated fuel, a clogged fuel filter, a dirty air filter, a malfunctioning carburetor, or a faulty spark plug. Check these components to ensure they’re clean and in good condition. If the problem persists, consider taking it to a professional for further inspection.
How do you fix a lawn mower that won’t stay running?
To fix a lawn mower that won’t stay running, check the carburetor for clogs and clean it if needed. Replace stale gasoline with fresh fuel and inspect the spark plug for wear or damage. Ensure the fuel cap vent is clear and the air filter is clean to prevent airflow issues.
How to clean lawn mower carburetor without removing?
To clean a lawn mower carburetor without removing it, spray a carburetor cleaner directly into the intake while the engine is off. Allow the cleaner to break down debris, then start the engine to flush out any remaining residue. This method is effective for light cleaning but may not work for heavy buildup.
How often should I replace my lawn mower air filter?
It’s recommended to replace your lawn mower air filter at least once per mowing season or every 300 hours of use, whichever comes first. If you mow in dusty conditions, you may need to replace it more frequently. A clean air filter ensures proper airflow and prevents issues like the mower stalling or running inefficiently.
