I have a 9N with a single terminal generator that is overcharging. When you increase the RPM of the engine, the ammeter will climb with the rpm of the engine. If you open it to wide open, the ammeter shows that it is neat 20a charging. Also when it is overcharging like that, the engine runs really bad until you throttle it down, and may even stall!
Does this sound like a voltage regulator, or the generator its self? Note, I haven't tried adjusting the screw on the back of the generator, still working on getting some of the paint off so i can turn the screw!