Try flashing it's field. Disconnect both dyno wires, ground the F wire and touch the D wire to the fully charged battery for one second, that is also grounded to the bike. (F to grnd. >12 ohms/ D to grnd. >1.2 ohms)
Sometimes just cleaning terminals inside the headlamp, for example, can do wonders. Brushes?
Sometimes just cleaning terminals inside the headlamp, for example, can do wonders. Brushes?