Offhand, it sounds like the ignition converter unit is not putting out enough current to the primary coil windings.
Does your battery have sufficient voltage?
It should be around 13-13.5V when fully charged.
If it's at 12V, it considered low, and if it's at 11V, it's considered dead.
Unfortunately, there's no troubleshooting steps to test the converter unit.
Only, the ignition pulse generator on the alternator cover, and the ignition coils.
I'd check with Ben at RC51Parts.com to see if he has a used one.