1980 xs250se low miles as it has been sitting. 13.6v at 4000rpm, 12.9v at 4000rpm with the lights on. Changed the reg/rec to single unit from the 2 solid state items (xs750/850 item). 4ohm resistance between the white wires, 0ohm between brown and green.
I am not sure how these generate power, but is the rotor supposed to be a permenant magnet, or is it charged by the inner stator? (brown/green wires).
anything else I can check before I go nuts with a sledge hammer?
Air leak if there are no cable/carb issues.
Could be a gasket, carb rubbers, even the crank seal behind the mag. get squirting with wd40, that will show if its a gasket/seal leak.
One thing you can rest easy on, we know exactly what bike your talking about, many of us have had one for years. I got mine 30 years ago.