It seems that 06 and 07 YZ's have a low end stumble. I have four rides on my 07 Yz , have been changing pilot and needle jet with not much success. Fuel screw adjustments are not the answer,it still stumbles off idle. This last ride it's getting annoying. Have read the post about Zip TY and ap mode, have three big ride coming soon I can't send the carb to any one, I need it! Can't believe you have to have some mod to fix this. Has anyone tried Powernow? Or have any other answer?