Posted July 25, 2011 - 08:23 AM
This has been a problem for other posters, and it was so easy, made for a real " I never thought of remembering that?" kind of epiphany.
Try with your gas cap off, or the vent line off. That can and will cause the symptoms your having. If you have ridden it since then, which you have not, it would have stalled as well. If the one way check valve in the vent line, line itself is clogged (or top hat vent like I have had go bad) it will stick and clog, and it will hold back enough fuel by vacuum to cause the engine to stumble like this and stall because gravity will not be enough to fill the float. It has even caused FI issues as well by holding back volume of fuel to the pump input after 60 sec or more.
The second one involved my own bike, and that was a stator in my 2008 KX450F. It never overheated, but all KX450F run hot and well, repeated heat cycles, time, caused mine to lose magnetism, even after everyone claimed mine was a fixed stator, or shouldn't happen with my version stator and year bike, it still happened. Would start some times one or two kicks, run and stall, flame out way too many times. Other symptoms as well.
New stator and the bike kicked tail once more, and never had an issue since. Also take your ECU out and check for cracks in the epoxy from time, that water may have seeped in through and for any cracks or shorting of your coil and high tension sparkplug lead. I doubt this would be an issue though.
Try a new stator from a dealer and check the gas cap vent.