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How to Fix a Flooded Lawn Mower Engine

If you have a gasoline-powered lawn mower, sooner or later the engine will become flooded. A flooded engine is the most common reason why a lawn mower engine won’t start. When the engine is flooded with gas, the carburetor can’t get enough air and the engine fails to crank. You can usually fix this problem yourself using a few simple steps. If your engine is flooded severely, you may need to remove the air filter and allow the gasoline to evaporate before your engine will start again.

Try the ‘Quick Fixes’

Set the throttle to the closed or “stop” position. Yank the starter cord or turn the engine about six times to create a vacuum and clean the extra gas from the lawn mower’s engine. Try to start the engine.

Try turning the mixing screw or needle valve if the lawn mower still won’t start. Turn the screw ¼ of the way to the left, and then try to start the mower. Turn the screw a second time if this doesn’t work and try to start the engine again.

Turn the mixing screw or needle valve 360 degrees to the right (clockwise) if the mower still won’t start. Try starting the engine again.

No Luck? Open the Butterfly Valve

Access the lawn mower engine and take out the air filter from the carburetor. Remove the filter using a screwdriver.

Insert the screwdriver into the carburetor barrel and into the butterfly valve to prop the valve open. Try to start the engine several times until it cranks.

Remove the screwdriver from the valve and carburetor barrel after the engine starts. Put the air filter back into the engine.

Still Won’t Start? Remove and Dry the Filter

Remove the air filter and allow it to air dry. This can take anywhere from one hour to several hours, depending on the outdoor humidity.

Place the air filter back into the engine after it has dried completely.

Try to start your lawn mower. If engine flooding was the problem, your lawn mower should start now.


If your lawn mower still won’t start after trying these techniques, it likely has other problems. For mowers with a condenser and points that don’t have electronic ignitions, these parts likely need replacement.


When working on the lawn mower’s carburetor, always keep your face and hands away from the carburetor when attempting to start the engine.

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