Seems like you checked everything,
..so all that leaves is a bad earth to the frame. Or your reg/rec unit is knackered. Or your ignition wiring is broken at the headlamp / switchgear.
Or you've got a crappy safety cut out somewhere like the side stand.

My bikes:

CB50J
Vespa 100
Kwak z250 single
Kwak z400 twin
Kwak GT 550/5
Honda 400/4
Honds Cd200 benly
Yam XS850 triple
Yam xs650 twin

I know my crappy old jap bikes.

Put some decent tyres and flat bars on, and teach yourself to ride a bike with a bit of torque instead of a load of revs.
(CADmonkey rollllllllled another one, just like the other one, Sun 7 Nov 2010, 12:22, Reply)