help with understanding how this 50cc fires? (ignition)

[ry57pont]

Help, i have a nephew who is a little motorhead, he is installing a 50cc engine (yamaha) into a bigger dirtbike that he bought from the junkyard so he can legally ride on the street.
We are trying to resurrect this and he had no wiring harness. so...

for the ignition i suggested we use a HEI 4 pin ignition module and a can coil like i did for my 2 stroke golf cart, seemed simple and works well on my cart...

i wired it all up just like my golf cart and now i get 2 sparks per stroke, one up and one down.

when i pulled the flywheel (see pic) there are 4 magnets on the flywheel and one induction coil on the plate for its original ignition. how did this work when new? how could the ignition pickup coil differentiate between flywheel magnets to determine how to fire on TDC? sorry if this writeup is confusing, i dont know how else to explain it.

https://i62.tinypic.com/bg8k68.jpg

https://i57.tinypic.com/beiv43.jpg

https://i61.tinypic.com/k55sn4.jpg