When your lawn mower engine turns over easily, but won't start, you will have to troubleshoot the cause of the problem. Small engines rely on three key components: air intake, spark and gas. If one of these things is missing or broken, the engine will most likely not start.
Unscrew the air filter cover from the side of the lawn mower engine with the screwdriver. Pull out the old dirty air filter and replace it with a new one and tighten the cover back on.
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Pull the spark plug cap off of the spark plug on the front of the engine. Fit the proper sized socket on the spark plug and unscrew it with the socket wrench. Finger tighten in a new spark plug. Place the socket on the foot-pound torque wrench and tighten the spark plug in at 15 foot pounds.
Follow the fuel line under the gas tank to the side of the carburetor. Locate the screw under the carburetor holding on the fuel bowl. The fuel bowl can get gummed up with old gas and prevent the gas from entering the piston.
Unscrew the fuel bowl with the screwdriver. Pull it off and dump out any old gas in it. Spray carb cleaner into the bowl and onto the float and valve area above the fuel bowl. Screw the fuel bowl back on tightly.