These bikes have a CDI system.
You have spark plug, ignition coil, CDI box, Stator
with a exciter coil and a pulse coil.
If your spark is weak it could be any of these
components or short in the stop or kill switch.
The ignition switch may have a kill wire also.
These can usually just be disconnected to test
them for problems. The ignition components
would have to be checked or replaced one at a time
to find the problem.
Good thing is the parts are very inexpensive for these
machines. A 5 pin CDI box is only about five bucks.
Ignition coil is maybe ten bucks and the whole stator
with pulse coil attached is about forty dollars.
Double check your parts to make sure they look the same
if you order anything.
You can also get a flywheel puller and check the flywheel for
rust or a stripped key.
Sometimes you can have a bad spark plug cap or plug.
Also check the connectors to each ignition part for problems.
Let me know if you need other info.