Just bought an 06 YZ450F off the showroom floor at a dealer nearby, and took it out sunday to Ocotillo for break in. After riding it around the camp for a while, with it running perfectly, seating the brakes and working the throttle up/down, I took off with my buddy and his wife and kids. We were taking it easy, cruising the trails, and jumped off into a wash with some more challenging terrain, when suddenly the bike died on me. I started it up and it was running very rough, wouldn't idle and I had to keep the revs up. So I caught up with them, and it was surging and sputtering alternately. I hit some deep sand and it surged suddenly, pushing me almost into a fence before I caught it and then it sputtered in the soft stuff, putting me down, and it died. Like I said, it was soft, but I still hurt my knee a little, so I'm walking the pain off, and trying to figure what the heck was up with my 15 minute old bike. Fuel was fine, same batch I had filled my truck up with before leaving from Shell, 91 octane, so that wasn't an issue. Elevation not significantly different either from dealership and Ocotillo. Then we tried starting it - would not start, either w/ and w/o hot start engaged. So we tow started it and it was rough - barely stayed running with constant revving. I just said I'm going back to camp, and barely nursed it home down shell reef expressway, surging and stuff the whole way, hard to keep it upright when the terrain got rough and i had to back off the throttle and it wanted to die on me. So I just forgot about it until the morning when I started it, on the first kick, but it sounded rough again, so I killed it. Took it back to the dealer today and they are mystified too. It backfired on the first and started on the second kick, but still sounded rough. They are going to get into it, but I'm not happy with the thing. For one, it hasn't had 1/8 of the time for break in and it's already screwed up? I'm not sure I like the chance of the thing getting broken in right, and what the future portends. Anyone else have a similar issue? If the thing doesn't come back perfect, I'm considering invoking the lemon law and asking for a new one. It shouldn't have happened, these bikes are bulletproof for the most part.