Right now I've got a 2007 YZ250 smoker. I like the bike, but I want something different (been on a 2-stroke for five years). I really want to stick with a Yamaha, so I'm leaning towards a YZ450F. I've got a couple questions. First is jetting. Nothing worse than buying a new bike and chasing down good jetting specs just to get it to run. Do they come fairly close stock (sea level-4000ft)? I haven't touched the jetting on my 2-stroke, its been great from the factory. Next is valves. Do you they need adjusting right after break-in? And then what is considered normal intervals? I'm a slower mid-pack B-level hare scramble rider, so I wouldn't beat on it too bad, say compared to an expert MX'er. How about overheating? Do they puke fairly easy? Like I said, I ride woods, and I'm not the fastest. I never boil my 250 over, but I know big 4-strokes produce a lot more heat. I had a liquid cooled XR650R that never boiled on me, but MX 450's are a whole different animal. Thanks!