I followed the advice given in the article on GB500 tuning.I fitted two base gaskets and used a 600 head gasket.It kicks over fairly easily when cold,but gets noticably stiffer when hot.The head showed signs of damage at some time,and one exhaust valve seat had been changed.I presume the seat and the cam were changed after the blow-up.The cam seems original,not reground.Before I stripped the top end,the engine was reluctant to rev out.It would pull six in 4th easily then run out of breath.It was happy to stay at 80 as long as the road allowed,but the most I ever saw,after a good run-up,was about 90.With hindsight,I presume that was a combination of a mild cam and a knackered piston.I'm not too concerned about top speed-I have another bike for that,but I would like it running correctly.I quite like the grunt of the engine as it is now-loads of torque from low revs in any gear.The clutch is now a problem - new plates,heavy duty springs,or both???Would I lose much of the bottom end if I fitted an XBR cam?