There are other possibilities to make a CDI unit

1 - Wind your own HV coil with as much windings if you can.
2 - Build a pcb with Thyristor triggering
3 - Find the correct timing for the spark

One drawback is, the unit fires twice per revolution. It is also called "wasted spark" ignition

Another approach is to fit a CDI unit from a Yamaha PW50 or PW80 bike.
For this you have to make an adapterplate to fit on the FS1

Also this produces a "wasted spark"

Testplate to figure out the exact spark timing, cut on the waterjet

The end result

The PW50 cdi mounted on the adapter plate
On the lathe I scraped off a tiny bit from the coils, so I could use the original flywheel.

The homemade HV coil