Re: 1974 115 hp evinrude
First, there are the requisite compression test and spark test.
Then, though there is a dearth of information to work with, start with as complete as possible a cleaning of all of your connections relative to the ignition. That means disconnect, thoroughly clean and reconnect. Be especially careful with the ground wires. Examine the ignition coils for any signs of heat damage such as cracks or discoloration.
You may wish to attempt to observe the engine running in the dark to see if there are arcs. Also make sure that your spark plug wires are not close to other wires.