ok.. the gasket on the cylindar head, was the gasket damaged? if it was it lost compression.. easy way to check for that is seeing if its been leaking oil, and the ajuster screws on the carburator.. it is probably possible it just isnt getting the fuel it needs at high rpms. or its flooding the carbs, just turn the screws all the way in.. and if its a twin the right cylindar should be a turn and a half more then the left. and the left should be three turns out.. if its any more then a twin its complicated, and i couldent tell you what to do.. but your owners manual will no, oh and about the valves.. do you hear a ticking? that gets worse when you rev up, adjust the intake for 6000ths and see if that solves your problem and 5500ths on the exahst.