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Somebody mentioned the valves being damaged when the bike is revved much past redline.
If the valves float at high rpm, they will bounce, 'tulip" and sink into the valve seat.
You can catch that if, when checking valve clearance, you find that the clearance is decreasing over time.
The solution is to stop revving it so high, increasing spring preload with shims (that rarely fixes it), replacing the valve springs with stronger springs (the usual solution).
If the valve springs are strong enough to keep the valve from floating at high rpm, the valve clearance will stay pretty much the same as when you set it.
If it was mine, I'd bump up the compression with stock bore or +2mm pistons, mill the head, port the head, bump up only the intake cam, install a programmable ign box
Dial the cam timing in for the desired powerband (dyno work), dial in the carbs, inc MAJ work.
Budget job? Mill and port the head, adj ign timing, dial in the optimal timing for the stock cams, dial in carbs.
Marc Salvisberg
Factory Pro Tuning
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