My brother in law and I were helping a friend of ours install a JD Jet kit on his brand new WR450. We removed the snorkel, took out the exhaust baffle and installed the blue needle, 4th clip from the top and the #170 main jet and replaced the pilot jet with the one in the kit, #45 I think. Elevation is 600 ft., temp around 65 degrees, MSR fuel screw, 1.5 to 2.0 turns out. The bike runs fine and response is good, but on decel or after a quick rev, the engine sounds like it's missing and makes not a backfire but a "FFFFT" sound. He didn't want the AIS removed so we left it. I don't remember the JD instructions saying to remove it. Checked carb intake boots and they are tight, no popping on decel either, just that occasional "FFFFT" misfire. Thanks!