Lawnmower engines are small in size compared to automobile engines, but they can be trickier than a vehicle engine when it comes to diagnostics. A push-mower or basic riding mower is usually equipped with a two-stroke or four-stroke engine, containing one or two cylinders. An engine that will not start could be the result of a multitude of symptoms, ranging from a bad spark plug to bad fuel. Adding starter fluid directly to the engine can help you diagnose why your lawnmower will not start.
Remove the air filter housing cover from the mower, using a screwdriver or Torx driver to loosen the mounting screw. For some models, you will need to remove the upper plastic engine cover, using a 3/8-inch drive ratchet and socket. Remove the air filter from the housing.
Remove the mounting hardware from the air filter housing, using a ratchet, screwdriver or Torx driver. Remove the air filter housing completely from your mower's engine.
Spray a light dose of starter fluid directly into the carburetor chamber of your mower. Set the engine speed to the midpoint, if the idle is adjustable, by hand. Set the engine choke to full choke, if equipped.
Start the mower by pulling the starter string or turning the electronic starter key. If the lawnmower starts for less than three seconds and then stalls, the carburetor needs to be adjusted, cleaned or replaced. If the mower starts for more than three seconds but less than 30 seconds, you may be looking at a case of bad fuel or water-saturated fuel.