So here's the news. I finally picked up my 450 from the dealer Thursday and had it at Dumont Dunes all weekend. Dealer repaired as per instructions from a Yamaha representative who was there. Dealer states Yamaha feels it is being caused by jetting that is too lean, causing a backfire during e-start that shears the key. They said they rejetted the carb and installed a stronger woodruff key. The part number for the key on my receipt is 90280-03001-00. I'm curious about whether this is in fact a new part number compared to the old key. My receipt also shows they replaced the spark plug, part number CR8E, an NGK plug. I don't know what they jetted my carb to but now it runs like crap on the low end. It ran great opened up on the dunes but it would not idle and wanted to die whenever I was coming to a stop. Furthermore, I could only start it with the cold choke even after extended periods of wide-open riding. (It was about 50-60 degrees up there, but I wouldn't think that is cold enough to require the cold choke after long riding). On the other hand, I used the heck out of my e-start, way more than I did before the initial key break, and I've had no problems. So, now I need to figure out my jetting to get that bad boy running like it was meant to.