How to Fix a Flooded Engine Lawn Mower?

The satisfying roar of a freshly-started lawn mower is a summer soundtrack. But what happens when that roar turns into a sputtering cough? A flooded engine is a common lawnmower problem, often caused by excessive starting attempts or a faulty carburetor. This can leave you with a frustratingly immobile machine and a growing lawn. But don’t despair! This guide will walk you through the steps to troubleshoot and fix a flooded engine lawn mower, bringing your trusty machine back to life. We’ll cover identifying the signs of a flooded engine, understanding the causes, and the step-by-step process of fixing the issue. Let’s get your lawnmower running again!

A Flooded Engine: Understanding the Issue

A flooded engine occurs when excess fuel accumulates in the combustion chamber, preventing the spark plug from igniting it properly. This results in a sputtering or coughing sound, a lack of starting power, or even a complete inability to start the mower.

Signs of a Flooded Engine

The following signs indicate that your lawn mower might have a flooded engine:

  • Difficult Starting: You struggle to start the engine, even after multiple attempts.
  • Backfiring or Popping: The engine sputters or backfires when you try to start it.
  • Fuel Smell: You detect a strong gasoline odor coming from the engine.
  • Wet Spark Plug: If you remove the spark plug, it might be wet with gasoline.

Why Does My Lawn Mower Engine Flood?

Several factors can contribute to a flooded lawn mower engine:

  • Excessive Starting Attempts: Repeatedly cranking the starter without success forces more fuel into the combustion chamber, leading to flooding.
  • Faulty Carburetor: A malfunctioning carburetor can overfeed the engine with fuel, resulting in a flood.
  • Fuel Line Issues: A damaged or blocked fuel line can restrict fuel flow, causing it to back up into the engine.
  • Choke Misuse: Leaving the choke engaged for too long can lead to excessive fuel intake and flooding.

Step-by-Step Guide to Fixing a Flooded Engine Lawn Mower

1. Remove the Spark Plug:

  • Locate the Spark Plug: The spark plug is usually located on the top of the engine, near the cylinder head.
  • Remove the Spark Plug: Use a spark plug socket wrench to loosen and remove the spark plug.
  • Inspect the Spark Plug: Check for excessive fuel deposits or a wet condition on the tip.

2. Dry the Spark Plug:

  • Clean the Spark Plug: Use a wire brush or a cloth to remove any debris or fuel residue from the spark plug.
  • Dry the Spark Plug: If the spark plug is wet, allow it to dry completely in the air or use a hairdryer on a low setting to speed up the process.

3. Clear the Cylinder:

  • Turn the Engine Over: Manually turn the engine crankshaft a few times to clear any remaining fuel from the cylinder. You can do this by inserting a screwdriver into the spark plug hole and rotating the crankshaft.
  • Reinstall the Spark Plug: Once the cylinder is clear, reinstall the spark plug and tighten it securely.

4. Try Starting the Engine:

  • Start the Engine: With the spark plug installed, try starting the engine again.
  • Adjust the Choke: If necessary, adjust the choke lever to the appropriate position for cold or warm starting.

5. Troubleshooting and Further Steps:

  • If the engine still won’t start:
    • Check the Fuel Line: Ensure the fuel line is free of blockages and is properly connected.
    • Inspect the Carburetor: If the carburetor appears to be malfunctioning, it may need cleaning or replacement.
    • Test the Spark Plug: Use a spark plug tester to ensure the spark plug is functioning correctly.

6. Prevent Future Flooding:

  • Avoid Excessive Starting Attempts: If you can’t start the engine after a few tries, stop and wait a few minutes before trying again.
  • Use the Choke Correctly: Engage the choke only during cold starting and disengage it once the engine starts running smoothly.
  • Maintain the Carburetor: Regularly clean and inspect the carburetor to prevent fuel buildup and ensure proper operation.
  • Store the Mower Properly: When storing your lawnmower, drain the fuel tank and run the engine until it stops to avoid fuel buildup in the carburetor.

Additional Tips

  • Safety First: Always wear safety glasses and gloves when working with gasoline-powered machinery.
  • Consult Your Owner’s Manual: Refer to your lawnmower’s owner’s manual for specific instructions and troubleshooting tips.
  • Professional Help: If you’re unsure about any of these steps or if your mower continues to have problems, consider taking it to a qualified lawn mower repair technician.


A flooded engine can be a frustrating setback, but with this guide, you have the tools to troubleshoot and fix the problem effectively. By understanding the causes, following the step-by-step instructions, and implementing preventative measures, you can restore your lawn mower to its full power and keep your lawn looking pristine. Remember to prioritize safety and consult your owner’s manual for specific guidance. With a little know-how, you’ll be back to enjoying the satisfying roar of your lawnmower in no time.


What is a flooded engine in a lawnmower?

A flooded engine in a lawnmower means there is too much fuel in the combustion chamber. This happens when the carburetor is not working correctly or when the choke is left on for too long. This excess fuel prevents the spark plug from igniting the fuel and air mixture, resulting in a “flooded” engine that won’t start.

You can identify a flooded engine by the smell of gasoline and by noticing that the engine struggles to turn over. The spark plug might also be wet with gasoline.

How do I know if my lawnmower engine is flooded?

Several signs can indicate a flooded engine:

  • Strong smell of gasoline: If you smell gasoline coming from the engine, it’s a strong indicator that the engine might be flooded.
  • Engine struggles to turn over: The engine will crank but won’t start, as the spark plug cannot ignite the excess fuel.
  • Wet spark plug: A flooded engine will often have a wet spark plug due to the excess fuel.

How to fix a flooded lawn mower engine?

Fixing a flooded lawn mower engine is a simple process that involves a few steps:

  1. Turn off the fuel supply: Locate the fuel shut-off valve and turn it off to prevent more fuel from entering the engine.
  2. Remove the spark plug: Remove the spark plug to release the built-up pressure in the cylinder.
  3. Dry the spark plug: Clean the spark plug with a rag and ensure it is completely dry. You can also use a hairdryer to speed up the drying process.
  4. Reinstall the spark plug: Reinstall the spark plug and tighten it to the correct specifications.
  5. Start the engine: Try to start the engine. If it doesn’t start immediately, try again after a few minutes, allowing the excess fuel to evaporate.

What if my lawnmower still won’t start after fixing a flooded engine?

If your lawnmower still won’t start after fixing a flooded engine, you might have a different issue. Here’s what to check:

  • Spark plug: Check the spark plug for damage or wear. Replace it if necessary.
  • Fuel lines: Inspect the fuel lines for blockage or leaks.
  • Air filter: Ensure the air filter is clean.
  • Carburetor: Check the carburetor for any issues, such as a faulty float valve or a clogged jet.

How to prevent a flooded lawn mower engine?

Preventing a flooded lawn mower engine is vital. Here are some helpful tips:

  • Use the choke only when starting: The choke enriches the fuel mixture, so only use it when starting the engine. Turn it off once the engine starts.
  • Avoid overfilling the gas tank: A full tank can put pressure on the fuel system and increase the risk of flooding.
  • Store your lawnmower properly: Always store your lawnmower with the fuel valve turned off to prevent fuel from leaking into the engine.

What are some common causes of a flooded lawn mower engine?

Several reasons can lead to a flooded engine in a lawnmower:

  • Faulty carburetor: A faulty carburetor might allow too much fuel to enter the engine, causing flooding.
  • Clogged air filter: A clogged air filter restricts airflow, which can lead to a rich fuel mixture and flooding.
  • Incorrect fuel mixture: Using the wrong fuel mixture can cause flooding.

Can I fix a flooded lawn mower engine myself?

Yes, you can fix a flooded lawn mower engine yourself. It’s a simple process that involves a few basic steps.

However, if the issue persists, or you’re uncomfortable working on the engine, consider taking your lawnmower to a qualified technician for repair.

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