I recently purchased a new 07 yzf 450 from a local dealer. I have had the bike about a month with the same problem. It has a hesitation with a blip of the throttle and it pops like crazy when you let off the throttle. I have gone through the carb and found some trash in the bowl, cleaned it all up blew out every orifice and reinstalled it. It runs great, but it annoys me the way that it does not rev cleanly and then pops off throttle. I have adjusted the pilot screw and it idles better at 3.5 turns out from seat and I think I need to go to a bigger pilot jet. Bike is completely stock. 160 main jet, 45 pilot jet and the clip is in the 4th position. Any opinions would be greatly appreciated. I have also read a little bit about the zip-ty carb mod and would like to hear some more input on that as well.