What Causes Lawn Mowers to Stall?

Low Fuel

• Start with the easy fix. Remove the cap from the fuel tank and look inside. If you can’t see any gasoline sloshing around inside, the mower may have run out of gas. When the gas is very low or empty, the engine will stall because it is missing a required element. Simply pour more fuel into the tank and start it up. Bad fuel, such as gasoline that has been contaminated with water, can also cause stalling. You’ll have to siphon the tank empty and put in fresh fuel to fix that problem.

Air-Fuel Mixture

• The small engines that power lawn mowers require a specific air to fuel ratio to run smoothly. If the fuel is too lean, meaning there is too much air, difficulty starting the mower, stalling and rough idling may be problems. These things may also happen when the choke is stuck in the open position. When the fuel mixture is too rich, meaning not enough air, the engine may stall as well. The choke on the mower should be in the closed position to start the engine and then adjusted to run smoothly. But if the choke is stuck in the closed position, it will make the fuel mixture too rich and the mower won't start or will not keep running.

Grass Clogs

• When you are mowing thick grass or grass that is particularly moist, the grass can clump and get stuck under the deck of the mower where the blades spin. Often the grass will get stuck around the area where cut grass is ejected from the side of the mower and will plug the hole, which causes more grass to build up under the deck and will eventually impede the movement of the blades. This clog will bog down the mower and can cause it to stall. If this is happening, you’ll have to turn off the mower and clear out the grass. You may have to adjust the blades higher or mow much slower over these thick or wet areas to prevent stalling.

Air or Fuel Filters

• Air filters and fuel filters on lawnmowers remove unwanted materials from the airflow or fuel lines of the mower. Eventually they get dirty and can become clogged if they are not replaced. If an air filter becomes clogged, it will prevent the proper amount of air from reaching the carburetor, and the mower will not run properly or may stall. If the fuel filter is clogged, it will not allow gas to reach the engine and the mower will stop running.