my son has a 90 kazuma it usually starts great, once or twice it was hard to start i changed the plug and problem solved. this time it didnt help the spark looked weak then would fade to no spark at all. I ordered a coil but still no spark. I put a battery charger on it prior to all of this. any advice?

 

might have bad plug wire. your battery just runs starter. check and see volts running thru system. could be easy fix with bad ground somewhere. your stator,like altenator on car. could be shot.