In Reply to: burnt valves posted by jonathan on December 26, 1999 at 00:53:15:
Lean engines don't burn exhaust valves. Rich engines burn exhaust valves, or engines with retarded ignition timing. When the exhaust valves become covered with carbon deposits, they no longer transfer heat to the seat rings; and they overheat.
Replace the valves, set the clearances, timing and mixture correctly and your problem will not come back.