You showed in a picture that I guess you were testing the spark using a spark plug, that works ok.
They also do it this way below on here.
I would test the power of the spark the Battery Ignition unit is making this way also.
Be sure the Cub doesn't roll while doing the spark test.
Remove the ignition wire from the center post on the distributor cap, and hold the wire by the insulation, with the metal end about 1/4" from bare metal of the engine block.
Be sure the transmission is in neutral, turn the ignition switch to on, and run the starter.
The spark should jump the 1/4" gap, and be blue or white. A yellow spark is weak, and needs improving.
The engine may not run, or run right, with a yellow spark.
Do the test in a building, or not in bright light, so you can see the spark well.
The battery should be fully charged for the spark test. Charge the battery if necessary.
A low output charger is better, it may take several hours to charge it.
