thuber

There are 2 brushes for the charging system under the side cover, they wear out, and it will cause exactly what you describe, most hard core 650 guys carry a spare set of brushes just in case, I fixed mine 1000 years ago on the side of the road, you cut the lead wire to the brush and wire it to the spring pushing on the brush, its very temporary but it got me home on a 3 hr one way ride.

or here: http://www.fjowners.com