I am currently having the exact same problem with 06 525 exc with JD jetting. Have changed needle to red in 5th position. Still popping on decel. I have 42 pilot as instructed by JD. Fuel screw all the way in or out does not seem to make a difference. I have not checked for air leaks yet. Planning on red RTV at joints and new gasket at head exaust flange. Also have 40 and 45 pilot jets on order. Also saw pictures at JD's websight showing pipes at flange at head not being parallel. That might worth checking. I am running out of ideas. Bike runs great except for decel popping and a little surging at about 10 MPH. Please let me know if you get anywhere.