WR250f 02' Tuning Question

okay. i like to think i have the WR250F pretty much sorted out.
looking at your specs, i am guessing you are running too rich, especially on the needle. i would first try dropping the needle 2 clips from your current position. this may make it crisper in throttle response too.
when you say it cruises fine until the gas is chopped, then it's time to look at your acc. pump duration/timing. thumpertalk.com has plenty of information on this issue. i would suggest you remove the air box boot from the carby, and wedge it back behind the frame. look down the throat and you will see a small brass jet sticking up. this is your acc. pump squirter. keep an eye on it while cracking the throttle all the way open, and hold it (engine off). if you have a squirt that is about 3 to 4 seconds long, then you need to do the BK mod. i'm guessing your squirt is too short, and i too had a short squirt problem. if it is the case (squirts for a fraction of a second), then you need to do the HB mod, which also involves doing the BK mod.
i have done the HB mod, and once set up, my bike runs great. i can crack the throttle open at any stage, and the engine will not hesitate. before, the engine would shut down.
i too have moved to YZ timing, and initially the problem became worse, but like i said it is fixed now. i would not go back to WR timing, as you don't need to. the only mod i would consider when going to YZ timing is the air cut valve mod, which is easy to do. i have been told you cannot do the mod while running WR timing, so it's up to you. oh, when you say back one tooth, i'm guessing you mean clockwise, right?