I'm getting back into riding, and my 2006 CRF250 hasn't been touched in two years. There's about 80 hours on the motor and it still runs, just not like it used to. I never rode it too hard, and the only thing I've done to it maintenance-wise is adjust the valves a couple times. Should I do the top end, or should I just get a new piston? Maybe a new chain and sprockets, too... I've been off the bike so long that I don't know where to start.