Back in the days when I owned one of these bikes, under hard acceleration it would jump out of 4th gear into neutral resulting in the engine over revving and the lock nuts vibrating loose on the tappets. Apparently some years later, I read that this was caused by the gear selector drum being worn and was quite a common fault. I've never heard it mentioned on here though, I am the only one who experienced this? My bike did have around 50,000 miles on the clock by this time. 

Russ