I picked up 1998 YZ400F a while back. Ive only ridden it around the block a few times. It seems to feel pretty good with the exception of some backfiring on decel, but whenever I stop... it wouldnt ido... it would just diel. The idol screw was all the way in and the rpm seemed to be at least around + - 1300 (no tach tough). I heard all kinds of great things about the ZipTy carb mod, and so I sent the carb to them to do the mod and check to make sure there where no other issues with the carb. Everything came back the other day, and the jetting is a 45 pilot and 178 main jet. The notes from ZipTy recommend going to a leaner pilot for starting. Other than that everything looked good according to them. I never really have any problem with the start though, just idoling. I got the carb reinstalled and upon starting her up... its the same thing. As soon as I stop playing with the throttle and try to let the engine idol, it just dies. The hot start is not stuck open or anything. Im not sure what to check next. Could the jetting be that far off? Or should I look somewhere other than the carb???