I too have the stuttering just as WR450SM did, only when riding slow under minimal to no load. However, I have continued to play with my jetting and it seems to of been minimized to the point where it is barely discernible. I know this makes no sense when looking at the data. My goal with jetting changes were only AP related, which is all the more confusing to me, as we know the AP has (darn well ought to) no effect at steady throttle. So here is my misguided and hare brained conjecture. If... at small throttle openings, most of the air velocity moving through the carb are at the bottom, is it possible... that some fuel is being sucked out of the AP nozzle, causing an occasional overly rich condition? I know the YZ's do not exhibit this condition but, I found the stuttering to become less of an issue the larger a leak jet I ran. Currently I am using a Merge adjustable one on the bike. As I said, these are all thoughts from a deranged and disturbed mind.