My 05 does this too, always has. The second I twist the throttle it's crisp and no stutter so it really hasn't bugged me too bad. However I was reading some other threads today about this and it was suggested to calibrate the TPS near the high end of the specified range. Mine was at the low end (.6v) so I set it at .73 but it's too cold and rainy/snowy to take it for a test ride. As soon as I do, I'll report back. Summit you aren't kidding about the weather:rant: Are you running the JD jet kit?what are you running in your carb? I too have the surge and notice it when I'm riding the roads. It sucks but I don't notice it on the trail. I'm running Year: 2006 Model (400 - 426 - 450): WR450 Cam Timing (WR/YZ): WR Main jet: 158 Pilot Jet: stock Leak Jet: #60 Starter Jet: 65 (Stock) Fuel screw (turns out): ZIP TY Fuel Screw 1.5 Turns Out (still tuning) Needle Model/Clip position: JD Red / 3rd Position Grey Wire Mod (Y/N): Y TPS Connected (Y/N): Y Airbox Snorkel/Lid (on or off): Off AIS Removed (Y/N): Y Airfilter Brand: No toil Exhaust Brand: FMF Q4 Average Altitude: 5000_9000ft Average Temperature: 70 - 85 F Degree of Satisfaction (0-10): 9 Additional Mods/Comments: I have been running red #4 in cooler temps but it was still to rich. I just put in the #60 leak jet and have eliminated the initial throttle hesitation. I will probably changing the main jet depending on temp. I have done the o-ring mod too. If I don't find this set up working I will be pulling out the JD needles and go with stock from here on out. I also have a quickshot 2 on the carb.