Might get a 450, have some questions.

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.


I've got an 06 450F and an 07 250 smoker. I still prefer the 250 for racing. Reliability on the 450F has been great. I've checked the valves once @ 10 hrs and am going to check them again this weekend. Jetting was pretty close, I went to 165 main/45 pilot. They do get hot and finicky when the weather is warm. Hard to beat the smoker for all around riding IMO.

Change the jetting. 165/45 works pretty good. When it cools down you might want to try a 165/48. I have never touched my valves. They state that you might have to adjust them, just so that you won't get pissed off if they do need adjusting. I don't think I have ever boiled over my bike. I have riden some pretty slow trails with people, and run pretty hard at the track, and no boil. If you have any concerns, just replace the coolant with engine ice. The YZF is a great bike, you won't be disapointed.

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