Generally, a lawnmower will shut off due to problems in the fuel or ignition system. These common problems can be fixed easily at home, saving money on repair costs. When the engine shuts off and won't start any more, check the fuel and ignition systems.
Air Filtration Problems
Before the air can mix with the fuel and enter the cylinder, it needs to be purified. Sitting above the carburetor, the air filter cleans out any particulate matter that would scratch the bore or the cylinder walls. However, when this filter gets too dirty to clean the air, the mower's performance will decline, and eventually it will shut off. Take the air filter out of its box and clean it according to your mower's operating manual. Some mowers will require washing the filter while, with others, washing will damage the foam element.
Fuel Supply Problems
Always check the fuel supply, before beginning a mowing job, as a low fuel supply will cause the engine to shut off. Make sure to only use fresh gas in your mower and never leave gas inside the tank for more than 30 days. If gas was left in the tank for winter or storage, the fuel will have dried out and gummed up the fuel system. This restriction in the fuel supply will cause the mower to shut off. Clean the fuel tank at the beginning of the season and replace the fuel filter every year. Check and replace the fuel hoses every couple of seasons or as needed.
If fuel was left in the tank over winter and the mower runs poorly, the carburetor is likely dirty and will need a thorough cleaning and inspection. All carburetors operate the same, but their designs vary widely. For this reason, draw a diagram of the carburetor before taking it apart so you can put it back together right the first time. Install a rebuild, more commonly referred to as a carb kit. This will solve most minor carburetor problems.
Spark Plug Problems
The spark plug will become fouled over time so replace the plug at the beginning of the season and as necessary throughout the summer. If the lawnmower shuts off, check the spark plug and replace it if the metal tip looks black or brown. Other ignition problems that can cause your lawnmower to shut off can come from the module or the plug wires. Leave all interior ignition system repairs to a professional as there is a high potential for electrocution.
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