upon repair and total dismantle it was found to be caused from carbon buildup from a new rider (my husband) lugging the engine. The same reason for the spark plug foul at 12.000 miles. Moral of the story: Don't teach someone to use a manual transmission 1) on a motorcycle 2) who can't tell the difference between normal and not normal sound or identify by sound when shifting is needed. I tried to explain when to downshift and upshift.....what worked is my mechanic telling him to make it sound as annoying to other people as possible....like he's racing all the time. Go figure. Thank you for all of your input!