My 426 is giving me fits. Having read all the posts from all the forums for the past 90+ days, I believe it's doing what most are refering to as "stumbling" or "hesitating", although my is actually dying. Have had the bike about 4 months now. It pulls & runs cleanly throughout the entire powerband, ONCE it's off idle and accelerating. The plug looks great; no carbon, not burnt, but a nice honey brown / tan color. Basically, if I "whack" the throttle open off idle, it will die or severely bog. Simply "blipping" the throttle to about 1/2 open will not cause it to die, but pinning it open will. If I bring the RPM up off idle with a more gradual opening of the throttle, then it's fine and I can open the throttle full from there. Where I'm having problems (maybe my old 2-stroke technique) is sliding the rear end into a low speed corner/berm, and then attempting to pin the throttle for the exit. Most the time it will die unless I back off very quickly. If I kill it, it will start right back up, so my guess is too much air (lean) with the carb slide all the way open. The accelerator pump appears to work fine, beginning to spray fuel at about 1/8 throttle. All jetting is stock. I have raised and lowered the needle, with no noticable changes, and as said previously, once "off idle" it runs great anyway. The stock fuel screw setting was 1 1/4 turns out. I had taken it up to 2 1/2 turns out with no change or improvement. I also changed the screw on the accelerator pump cam. Stock was 3 turns out. I could find no improvment by adjusting either in or out on the screw, and actually about the best I could find was the "stock" screw setting. For all those who have answered questions previously on what I hope is the same topic, is this the same problem everyone else seems to be having? I have ordered a Factory R&D P-38 kit in the hopes that it will cure (or at least improve) the problem. I have checked the ignition timing, and while not spot on, it is within the "H" band mark. I live in the Dallas / Ft Worth area of Texas. Four different dealers have told me four different things. Answers have ranged from "they all do it so live with it" to "you need to adjust the carb slide". Not a real confidence builder to shell out bucks here. Any hints or additional suggestions would be greatly appreciated. Also, if anyone in the DFW area can recommend a COMPETENT YZF mech / tuner, please send me his name. Thanks.