Lawnmowers are kings of the garden tool kingdom. No other machine makes yard work easier. The common mower engine propels the mower across the lawn, cutting grass faster than the old rotary models. The mower engine is a complex piece of equipment with many moving parts. If one of the parts fails, the brave lawnmower becomes a very heavy paperweight. Troubleshooting an engine properly may reveal that the problem is easily fixed or that it's time to get a new mower.
Confirm the engine has enough fuel and oil to run properly. Gas tanks have fill lines which you can check against, while the crankcase has a dipstick that indicates whether the oil is at the right level. Ensure the right oil is used for your engine.
Inspect the fuel to make certain it is fresh. Gasoline that has been in the tank for more than a month becomes stale and will not start the engine.
Turn on the ignition switch if your mower has one. Inspect that all safety devices are engaged, such as the handle safety levers. Engage the brake if necessary and ensure that the clutch is in neutral on a riding mower. Mowers turn on if the safety features are engaged properly. Ensure all safety wires are attached properly.
Remove the spark plug, and touch the end of it to a piece of metal to see if a spark leaps off it. Do this away from the mower. Replace the spark plug if it does not spark.
Probe the gap at the end of the spark plug using a spark plug gapping tool to make sure the gap is at the right height. Compare the measurement from the gapping tool against the mower manual.
Look at the air filter by opening up the air filter casing and removing the filter. Clean a foam filter using soapy water. Paper filters require replacement if dirty or clogged.