Hey guys, looking for some help here. I am a bike guy... Buddy has 05 450R, cylinder works 479 big bore, HMF full system, ported head, Twin air Powerflow kit, airbox lid removed, 50/50 VPc12 and 93 pump. Starting having trouble with it cutting out, not idling, stalling. Had an FCR off of 2002 CRF450, it leaked fuel with all new gaskets etc, were having problems, so went back to factory carb once we spliced the correct plug on, wiring is correct. Bike idles cold with choke, gets warm it wont at all, doesnt matter at all where idle screw is set, fully in or fully out. Backfires showing it is lean, I expect the pilot jet and maybe needle to be since this carb was jetted for stock motor plus exhaust/filter previously. We are running a 190 main right now trying to get it to pull up top, used to have I think a 175. It acts like a slow rev limiter, just stops pulling and bum..bum..bum slower than an actual spark cut. I dont know what his clip is set at or what his pilot jet is currently. We are 3 1/4 turns out on fuel screw, still backfires on decel so I know we need to go bigger there and in with the screw. We are 2000 ft elevation. Plan to check ohm reading on tps, manual says between 490-510 fully open I believe. Plan to pull ignition cover and be sure that flywheel etc is clean/debris free. He has a custom wiring harness built by I believe Derissi racing, Santo is the dudes name, runs GNCC. Not impressed as it came back with no loom, just electrical taped whole thing. We would rather not untape the whole thing shooting in the dark, but may come down to that. Plan to swap coil with good running 05 450r. Main question is, what size jets reccomended, any other things we should check. I usually am the best in the group jetting wise, but this thing has me stumped because it is so inconsistant, making me think its more spark related. An rpm/throttle range that worked day before in identical whether, will now cut and backfire/blubber next day. We are pulling hair out here!!! Sorry for long post, appreciate anyone who read the whole thing and has any info.