If you believe that your lawn mower does not have any spark, a thorough test of the ignition system is in order.
There are two main times that a lawn mower will not develop spark.
The first is during the initial startup and the second is after the lawn mower has been running for a while.
Let’s start with no spark on startup. You attempt to start the engine and believe that there is no spark. Obtain a spark tester and place it in line with you spark plug wire. Crank the engine over and see if there is spark. If you see a bright blue spark, then the problem is not ignition related. If you have no spark, disconnect the black or gray kill wire that is plugged into the ignition coil. With this wire disconnected, if the engine starts, you will not have a way to shut it off, so plan for that! If the lawn mower does start, then the problem is in the kill system circuit and that will need to be inspected to find out the source problem.
If the lawn mower was running for a while and then you lose spark, install the spark tester to determine if you have a no spark condition. If you have no spark, the most likely item that will cause this is a bad ignition coil. Replace the coil and retest the lawn mower for spark.