Motorcycle Repair: CT90 Charging Issues, charging systems, stator

Question
My 1972 CT90 K4 is having charging issues.  When at idle (with the headlight off) the voltage at the battery is around 6.5V.  But when I turn the headlight on at idle, the voltage drops until the bike stalls.  Once going down the road, the engine will miss at high RPM with the headlight on.  I have replaced the battery and rectifier, and checked the stator.  Is there somewhere else I could look?

Answer
Those charging systems are pretty simple.  The alternator does not put out enough current to charge the battery at idle.  If you rev the bike up to about 3000 rpm it should show a voltage increase.  If the battery has a full state of charge, the alternator will put out just enough current to keep it charged when the lights are on.  If the brake light is stuck on, the alternator won't keep up and the battery will run down.  If everything electrically checks out fine, my last suggestion is the flywheel.  I've seen a number of those which have lost their magnetism over time.  I don't know of a way to check it so I alway make sure the other components are good before I replace it.  

Good luck
Rich