Why Doesn't My Lawn Mower Start?

Air Problems

• For the gas to combust at a high enough temperature to power the piston and crankshaft, the fuel first must get diluted with air. Air needs purification before it can mix with the fuel, otherwise dust and other particles would scour the sides of the bore and ruin the engine. The air filter traps all particulate matter and needs regular cleaning. Without regular cleaning, the air filter gets blocked and air does not enter to mix with the fuel. Clean the air filter after every 10 to 15 hours of operation.

Spark Problems

• After the fuel reaches the cylinder, the spark plug emits a high-voltage charge, igniting the fuel. If the spark occurs at too low of a voltage or at the wrong time, the fuel won't ignite and the engine won't start. Spark plugs need replacing on a seasonal basis to keep the electrode gaps from get covered in carbon deposits. Other sparking issues include loose wires, faulty connections, damaged flywheel, discolored flywheel magnets and an old ignition coil. Allow a service technician to perform any ignition repairs because of the potentially lethal high voltage.

Fuel Problems

• Fuel must reach the cylinder not only at the right time, but also in the correct proportion for the required engine speed. If the carburetor can't pull gas into the carburetor, it may be impossible to start the engine. Fuel can leave behind corrosive and sticky deposits, which gradually clog up and stop the movement of the fuel. Fuel problems include dirty fuel tanks, plugged vent holes, dirty fuel filters, old fuel hoses and a dirty carburetor.

Other Issues

• More serious issues can occur in the interior parts of the engine, especially as the engine ages. These issues can cause major damage to the engine, which may require costly and lengthy repairs. These problems usually occur with a loss in the vacuum pressure needed to keep the moving parts moving. Air leaks can occur at many different points in the crankcase and carburetor. These areas need professional diagnostic pressure testing to locate the source of the leaks.