Ah, the venerable Yamaha XJ650. I had one myself a few years back. Solid, bulletproof reliability, and not a bad ride either. What killed mine in the end was the diaphrams in the carburettors perished, and Mr Yamaha wanted an arm and two legs for a replacement set. So I sold it to a friend who has a motorcycle wrecking business and bought an FZR750. FWIW, my friend still has a good supply of spare parts and he does ship worldwide, so if you need any parts I could put you in touch with him.
Mark aka Paulus