OMG
Take the mixture screw and turn it in until it lightly seats. Turn it out 1 turn. If this does not help, take out the 50! Put the 48 back in and turn it out to 2.5-3 turns. This is what you have to do, nothing else is the problem. Not gas, not your main, and unless the filter is caked with sand or mud...it's not that either. If you want to make the 50 pilot work, you must cut a few big holes in the airbow lid or take it off completely. An aftermarket filter may also be needed.
As far as the main goes, there is nothing you have described to help tune your main. If it seems fine until mid, then falls on it's face a little, or gags...go down on the main until it feels better. Try a 170 to start.
Sorry, I wasn't trying to be too big of an ares. Just tying to keep it straight.
TRX450R...Pulse Charger, 12.25 HH, HotCam S2, KW valves and springs, P&P, UNI filter, airbox outterwears, Woodward fuel screw, Denton stabilizer,ProArmor K/S, Elka Elite longtravel 17" w/dual linkage, Figair airbrushed hood, Holeshot fronts, Razr II's rears, AC Propeg nerfs, +1 1/2 stem, Armidillo skids.
And a very well modded 03 warrior, engine, suspension, etc