I think MaxPower has the only WR that does not do the 'stutter'. No amount of jetting changes improved mine. James Dean has done exhaustive work too in an attepmt to 'jet away' this to no avail. Using an oscilliscope, the erratic ignition pulses were recorded. A Vortex CDI was installed and even with it, on certain engine maps, the stutter remained. On one map, the stutter went away. Disconnecting the TPS (vis a switch) will not make go entirely way but improves it somewhat. The stutter is never noticed off road, only on road at steady throttle.
I must be really lucky then, my supermoto WR426 doesn't stutter at all. When I got the bike it did it a little bit but after jetting it correctly and adjusting the TPS (not disconnecting it) it was completely gone. This was when I had the original CDI as well, I only got the Vortex cause the original crapped out. Maybe it's a bigger problem on the later models?