I have alot of miles on my 07 650 H1 and have not adjusted the valves or even checked them. It runs great, no noticable engine noise change, spark plug is clean. Maybe it is time to check them. Do the valves tend to loosen or tighten? Like I said in a previous thread, I have 5000 miles on my Prowler and it runs the same as when I bought it brand new.