here is an idea. take the mixture screw and screw it in until it stops. do not over tighten. then unsrew it 2-1/2 turns out. that should give you a good starting point to see if it's a air/fuel problem. If that does not correct it I would see if there is something like a pick up coil that can be replaced. I am not familiar with the TTR series, but it sound like some familiar issues I have dealt with before.
good call, you need to get a feel for tuning that tho, not hard at all but for someone who loosened up his main jet it may be above your head lol, im jk. you need to play with the air fuel, it can make a diference.