Troubleshoot your Craftsman lawnmower to determine why it doesn't start. Several of the common causes are easy fixes. If you have difficulty locating the problem, take the mower to a small engine repair shop.
Check the air
Small engines mix fuel and air in the carburetor and inject it into the cylinder to burn. If the air filter clogs, the mix is too rich and the engine runs rough or does not start. Fix the problem by cleaning or replacing the air filter.
Check the spark
The spark plug provides the ignition source for the fuel-air mix. If the plug wire disconnects, it cannot fire. A dirty or fouled plug provides a weak spark or no spark. Check the connection. If the plug is connected, disconnect the wire and remove the plug from the engine. If it appears worn or dirty, replace it.
Check the gas
Make sure there is fuel in the tank. If the mower has been idle for several months, empty the gas from the tank and add fresh gasoline. As the machine sits, the more volatile compounds from the gasoline evaporate, making the mower more difficult to start. Tap on the side of the tank. If the fuel filter clogs, this often moves debris so the mower starts again.