Very rare that the internal Novi coils die. Check it with a ohm meter with the wire disconnected from the points and the iron core near the tail end solder (not on the solder but near it) it should be 0,5-1,0Ω ±10%
I would suspect the bonding strap (between the engine upper mount and the external coils lower mount stud) they are crap (replace it anyway with a new wire going from a intake stud up to the ext coil lower stud).
Next check the condenser (also a good idea to change anyhow to an external one mounted at the ext coil lower stud, wire the pigtail to the grey coil wire, disconnect the original), followed by the antiparasite plug cap (NGK LB05EP perfect substitution), then the external coil (if the external coil looks chalky or dry or has a crack replace it).
If your internal coil tests defective you need to google "bobine allumage" for Mobylette or MBK or AV88 (etc) and pick your favorite frenchie supplier.