I've read most of the threads on the AIS on the '05 WR450 so I do have the plug kit ready to remove the AIS. I'm just going to work on the jetting some more before I remove it. My thoughts are if the AIS is helping burn unburned fuel in the exhaust, maybe I can use that to get my jetting closer to optimal if I can eliminate more unburnt fuel (ie. if it pops less on decel with the AIS by just jetting, than I should get more efficiency and maybe better mileage). The odd thing is I was always used to more popping from a lean condition so move up the PJ to get rid of it. I had only slight popping with my stock 450 at about 70 degrees and 3000 feet. I put on the James Dean kit with the blue #3 needle/clip position and the 170 main jet like it listed in the instructions (was thinking of the red but thought it wasn't quite hot enough). The idle mixture screw I left stock at 1.5 (did put in a T handle but left it where stock was). Now I get huge backfires on decel after the rejet but it seems with the 170 main and the blue JD #3 it should be richer. My guess is I'm running too rich and excess fuel is coming through the exhaust and the AIS is helping to burn it up causing the bad popping. Since I've only changed the main and the needle, I'm going to try either dropping to the 168 main or putting in the red needle and see if it pops less. Hopefully I can get it dialed in on my next ride, then pull the AIS and plug it up. I may temporarily plug the AIS before removal to see how it works. I was able to ride 50+ miles with the stock setting without hitting reserve so I'll have to do another 50+ to see how far I can go with the new jetting. Any ideas or comments on the main or needle I'm running? It's starting to get 70+ where I ride so I think leaning it a bit won't hurt.