$400 is a good deal for you.
How far was the bike ridden with no valve adjustments before a valve failed?
the new bike 400 mile adjustment is the most important, and maybe again at 4000 miles, but after that they dont change much for many many miles.
Did the bike have any other mods? If someone modified the intake and exhaust and did not change the jets to match, then running the bike lean will also burn your exhaust valves.
EDIT: I see in your photo the bike does have an aftermarket exhaust, so running lean could be the cause of the valve failure, or running so rich the valve carbon built up to where they would no longer seat properly.
Last edited by KCW; 07-28-2017 at 02:06 PM.