How do you fix a flooded lawn mower?

A flooded lawn mower that won’t start is a common problem many homeowners face. Flooding occurs when too much gas fills the combustion chamber and prevents the engine from firing. Thankfully, fixing a flooded mower is usually a simple task. With some basic mechanical skills and troubleshooting, you can get your mower running again quickly.

What Causes a Lawn Mower to Flood?

There are a few typical causes of a flooded mower engine:

• Priming: Repeatedly pressing the primer bulb to start a cold engine can flood it with gas.
• Choke: Engaging the choke for too long when starting can also cause flooding.
• Dirty air filter: A restricted air filter prevents proper airflow, leading to a rich fuel mixture and flooding.
• Carburetor issues: A faulty float, needle valve, or diaphragm in the carburetor allows excessive fuel into the engine.

Any of these issues can cause the engine to be overwhelmed with gasoline, preventing ignition and operation.

How to Fix a Flooded Lawn Mower

If your mower won’t start and you suspect flooding, follow these steps to get it running again:

1. Remove the Spark Plug

The first step is to remove the spark plug, which allows you to check its condition and release any excess gas from the cylinder:

• Locate the spark plug on the engine block and remove the ignition cable.
• Use the appropriate size spark plug socket to unthread the plug.
• Inspect the spark plug – it may be fouled from the rich fuel mixture. A black, wet tip indicates flooding.
• Lay a rag over the spark plug hole and crank the engine over a few times. This will eject any excess gasoline from the cylinder.

2. Dry Out the Spark Plug

Before reinstalling a fouled spark plug, it needs to be thoroughly dried:

• Use carburetor or brake cleaner spray to remove any oil or fuel buildup on the plug.
• Use a wire brush or emery cloth to remove carbon deposits and debris on the electrode and insulator tip.
• Wipe the spark plug dry with a clean cloth.
• Allow at least 15 minutes for any remaining moisture inside the plug to evaporate before reinstalling.

Installing a wet spark plug will prevent the engine from restarting. Letting it dry prevents misfires.

3. Adjust Choke, Priming, and Air Filter

Before attempting to restart the mower, make adjustments to prevent repeat flooding:

• Choke – Make sure the choke lever is in the OFF position. Starting with the choke engaged will overload the engine again.
• Primer – Do not pump the primer bulb more than 2-3 times when restarting a hot engine. Excess priming causes flooding.
• Air filter – Inspect the air filter and clean or replace it if dirty. Restricted airflow causes rich fuel conditions.

Making these adjustments prevents the engine from getting too much fuel when restarting.

4. Reinstall Spark Plug

Once the spark plug is dry and any choke/primer/air filter issues are addressed, reinstall the plug:

• Thread the spark plug in by hand until snug to prevent cross-threading.
• Use the spark plug socket to tighten the plug to the torque spec in your mower’s manual (usually 20-30 ft-lbs).
• Reattach the ignition cable to the spark plug.

Your mower should now be ready to attempt starting again.

5. Attempt to Start the Engine

With the flooded engine primed and spark plug reinstalled, try to start the mower:

• Make sure the fuel valve is on and set the choke to OFF.
• Pump the primer bulb 2-3 times if the engine is hot, 4-5 times if cold.
• Pull the starter cord with a rapid, full arm stroke. The engine should attempt to turn over.
• Let the starter recoil fully between pulls. Don’t pull the cord again until it has retracted.
• If the engine doesn’t start after 3 pulls with no ignition, repeat the spark plug drying process.

If properly dried and primed, the mower should start within 3 pulls of the starter cord.

6. Keep the Choke Off Once Running

After starting the flooded mower, be sure to immediately turn the choke lever to the OFF position. Running with the choke on will overload the engine again.

Let the engine run for a minute to stabilize and heat up to normal operating temperatures. The mower should now be ready to resume normal operation.

What to Do if the Mower Still Won’t Start

If the flooded engine still fails to start after drying the spark plug and proper priming, further troubleshooting is needed:

• Install a new, known good spark plug to ensure ignition isn’t the problem.
• Check for spark by disconnecting the plug and grounding it while cranking the engine. No spark means a bad ignition coil.
• Verify fuel is reaching the carburetor by disconnecting the fuel line and catching gas in a container while priming the system.
• Remove the air filter and spray starter fluid into the carburetor throat while trying to start. This will help rule out fuel delivery issues.
• If problematic, the carburetor may need cleaning or rebuilding to address internal faults allowing flooding.

Use this structured troubleshooting to isolate the root cause if flooding fix attempts fail. In many cases, carburetor servicing will be required to get a balky flooded mower running properly again.

Best Practices to Prevent Future Flooding

While fixing a flooded mower is straightforward, prevention is ideal to avoid downtime and engine damage. Here are some best practices to avoid repeat flooding incidents:

• Only prime the engine 2-3 times when hot, 4-5 times cold. Excess priming overwhelms the engine.
• Engage the choke for no more than 30-60 seconds when starting. Leave it OFF when warm.
• Keep the air filter clean and change it regularly. Check it if flooding occurs.
• Replace deteriorated fuel lines that can restrict gas flow to the carburetor.
• Use fuel stabilizer in the gas and run the mower dry before storage to prevent gumming.
• Clean the carburetor annually and inspectFloats, needles, and diaphragms prone to cause flooding.

Adhering to these best practices will minimize flooding and keep your mower starting reliably season after season.

Conclusion

Fixing a flooded lawn mower is a relatively simple process of drying the spark plug, priming the engine appropriately, and troubleshooting other underlying issues. With proper drying time and fuel system adjustments, most flooded mowers can be restored to service quickly.

Preventing flooding is ideal, as gas-fouled engines are more prone to wear and damage. Follow recommended priming procedures, maintain a clean air filter, replace old fuel system components, and properly prepare the mower for storage. Adopting these best practices will minimize future flooding issues and lead to more reliable starting.