Lainaa:
I also suffered from this really bad vibration between 3000 and 4000 rpm. Having just had the bike serviced, I have discovered it is because an anti-backlash spring on the clutch basket is worn or broken. Apparently, it isn't too much of a problem to the engine, just so long as you can live with the vibration. The downside is that (surprise, surprise) you have to buy a whole new clutch basket (c. £350. Plus about one hour's labour) to get it fixed. I thin I will take the advice of our more spirited colleagues and keep the revs over 4000 and live with it for now...