Fix Flooded Lawn Mower

Smell gas? Mower cranking but not catching? You flooded it. Happens to everyone - you prime it too much, crank it a bunch of times, and now the cylinder’s swimming in fuel. The fix takes five minutes and you might not even need tools.

Table of Contents

• Signs of a Flooded Engine
• Quick Fix Methods
• Spark Plug Method
• Wait It Out Method
• Preventing Flooding

Signs of a Flooded Engine

How to Tell It’s Flooded

• Strong gas smell
• Engine cranks but won’t start
• Spark plug wet with fuel
• May see fuel in air filter
• Started to fire then died

What Causes Flooding

1. Over-priming - Too many primer pushes
2. Repeated starting attempts - Each crank adds fuel
3. Choke left on - Rich mixture floods engine
4. Carburetor issue - Stuck float/needle
5. Bad spark - Fuel enters but doesn’t ignite

[NEED IMAGE: Flooded lawn mower symptoms]

Quick Fix Methods

Method 1: Wait and Try (Easiest)

If mower just flooded from over-priming:

1. Don’t prime again
2. Move choke to RUN (not START)
3. Wait 5-10 minutes
4. Try starting without priming
5. May need 5-10 pulls

Success rate: Works for mild flooding

Method 2: Full Throttle Start

Some engines clear flooding with this technique:

1. Move throttle to FAST/HIGH
2. Move choke to RUN (open)
3. Pull cord continuously (10-15 pulls)
4. Engine should sputter then start
5. Let run to burn excess fuel

Warning: Engine may race initially - be ready

Method 3: Spark Plug Removal (Best)

Most reliable method for severe flooding.

Spark Plug Method

Step-by-Step

Tools needed:

• Spark plug socket (usually 13/16” or 3/4”)
• Ratchet
• Clean rag
• Wire brush (optional)

Steps:

1. Disconnect spark plug wire

   • Pull boot off plug
   • Move wire away from plug hole

2. Remove spark plug

   • Turn counterclockwise
   • Note plug condition

3. Inspect plug

   • Wet = Flooded (confirmed)
   • Dry = Different problem

4. Dry the plug

   • Wipe with clean rag
   • Clean electrode if fouled
   • Let air dry completely

5. Clear the cylinder

   • Keep plug out
   • Pull cord 5-10 times
   • Fuel will spray out - stand clear

6. Reinstall plug

   • Thread by hand first
   • Tighten snug (don’t overtorque)
   • Reconnect wire

7. Start without priming

   • Choke to RUN
   • Throttle to FAST
   • Pull cord
   • Should start within 3-5 pulls

[NEED IMAGE: Spark plug removal for flooded engine]

Cleaning a Fouled Plug

Severely flooded engines leave carbon deposits.

Quick clean:

1. Spray plug with carb cleaner
2. Scrub with wire brush
3. Dry completely
4. Check gap (0.030” typical)

When to replace:

• Electrode worn
• Insulator cracked
• Won’t clean up

Wait It Out Method

When Waiting Works

• Mild flooding
• No tools available
• Engine is warm

Procedure

1. Remove air filter cover (optional, helps evaporation)
2. Leave spark plug installed
3. Open fuel shutoff if equipped
4. Wait 15-30 minutes
5. Try starting with choke OFF
6. No priming
7. Multiple pull attempts okay

Speed Up Evaporation

• Remove air filter
• Remove spark plug (if possible)
• Point mower toward sun
• Open fuel shutoff

Preventing Flooding

Priming Guidelines

Engine Type	Prime Presses	Notes
Cold engine	3-5 times	Most engines
Warm engine	0-1 times	Often none needed
ReadyStart	0 times	No primer
Hot restart	0 times	Never prime hot

Proper Starting Procedure

1. Check fuel level
2. Set choke appropriately
3. Prime correct number of times
4. Pull cord smoothly
5. If no start after 5 pulls, stop
6. Wait or remove plug

Common Mistakes

• Priming repeatedly - Each pump adds fuel
• Choke always on - Only for cold starts
• Cranking endlessly - Stop after 10 pulls
• Ignoring no-spark - Flooding from lack of ignition

When Flooding Keeps Happening

Carburetor Issues

If mower floods without over-priming:

Check:

• Float level (stuck high)
• Needle and seat (worn)
• Float bowl gasket (leaking)

Fix: Clean or rebuild carburetor

Ignition Problems

No spark = unburned fuel = flooding

Check:

• Spark plug condition
• Plug wire connection
• Kill switch position
• Ignition coil

Choke Problems

Choke stuck closed causes flooding.

Check:

• Choke plate movement
• Choke linkage
• Auto-choke thermostatic spring

Related Guides

• Lawn Mower Won’t Start
• How to Clean a Carburetor
• Spark Plug Troubleshooting
• Briggs & Stratton Engine Problems

Summary

A flooded lawn mower is easy to fix. For mild flooding, wait 10-15 minutes and try starting without priming. For severe flooding, remove the spark plug, dry it, pull the cord to clear the cylinder, reinstall, and start. Prevent flooding by following proper priming guidelines and stopping after a few unsuccessful pulls.