I have a 2001 426 and I have to admit the bike ran great while the temperature was in the 60’s to 70’s. Once the 80’s and 90’s came around I have had to make some major changes in the pilot, main, fuel screw and clip position. I am riding this in Colorado currently with a 68 pilot, 152 main, 3rd clip position and the fuel screw at ¼ turn out. I can have the screw all the way in and it runs alright. I have good power throughout the low end, mid range and top end. It’s only on deceleration that I get an annoying backfire. I run the bike with a White Brothers R4 with the stock header. It seemed the backfiring started after putting on the R4. I went back to the stock pipe and its doing the exact same thing. Both pipe run the best with the same settings. I would have thought for sure one would run better one way and the other another way. I have replaced the CDI unit, cleaned the carburetor and checked for any leaks. Any ideas what would cause this? I always was told that the fuel screw should be 1 to 2 turns out. I can’t seem to get the bike to not backfire as much unless I have in fully closed to ¼ turns out. I am frustrated at the least.