First of all let me give the data of my YZ 250 F 08 model: Model (YZ or WR 250F):YZ250F 08 Timing (WR-YZ):YZ Main jet:170 Pilot Jet: 48 Fuel screw (turns out): 2 Needle model/Clip position: GYTR/4th Airbox lid (on or off):It´s an Yz Pipe: Complete Leovince X3 Ti Altitude where you ride:Sea level to 2, 3 km´s above see level of a bit more somethimes. Temperature where you ride:0 in the winter to 35celsius in the summer Have my bike for a year now and never had a single problem except when it camed but i put a smaller MJ and it was perfect since now. The problem started when i cleaned the carburator. After cleaning it i drove all day and all was ok but at the end of the day it was booging in low rpm´s so i check all the pieces in the carburator and jets and put a new GYTR needle. Everything is perfect with the bike, valves, piston, cylinder, all checked and some parts exchanged during the time i have it. So i put a GYTR needle with a Main jet of 176. At this moment i put a 170 Main Jet and it seems to be better. Yesterday i rode all day in a motocross track and the bike is fine but after riding for some time i went to some hills and i noticed that with inclination is when the bike fails. With no inclination all ok, with inclination not ok, when i have the thotlle in 1/4 or a bit more it chockes and real power only in high revs. Today i missed a XC event after doing pratices because it had too much hills and the bike was not ok...i am pissed as you guys can understand. Tomorow i will try a 168 MJ with the 2nd clip position but i am starting to think that i have a problem in the carburator but i don´t know how to say it in english "the ball"???? Tomorow i will meet my mechanic and make some tests on a nice hillclimb i kepp you posted. Opinions are obviasly welcome.