Thanks for answering about it being a USA Cub.
The way they say on here to check the spark is to pull the center spark plug wire out of the magneto cap, and hold it by the insulation, with the end of the wire 1/4" away from a place with no paint, on the engine block, turn the ignition switch to on, and run the starter, there should be strong blue sparks.
It should also have blue sparks if you remove a spark plug, and connect it to the ignition wire, set the bottom of it on a bare place on the head, and run the starter.
Yellow sparks are weak, and the engine may not run.
If the spark is yellow, the ignition points, condenser, or coil could need replacing.
New ignition parts can be defective, and not work right, something in the magneto might need replacing again, if it's not making blue sparks.
Below is a pic of the magneto drive, governor gear. It should be in this position when the engine is at number 1 cylinder TDC.
Sometimes people have the governor off the engine, and turn the gear to the wrong position.
The timing gears have marks to align them to the right position.
The 2nd pic, from TM Tractor, shows the gear teeth, and the timing mark, on the left side of the pic.
