Hi, Here is my story. I 've bought a wr250 2001 3 months ago and i had a unknown problem on it. One exhaust valve kept slacking. Tried hard to find the problem and i could'nt put 1000$ for a rebuilt just for that. Sold it and put just a little more money to get that beautiful almost new Wr450 2003. And here another hard to resolve problem with another WR..... First ride was yesterday. Bike is running well but 1/8 steady throttle sputter like crazy and seem to cut and go ( when i pull the choke the bike when to die when running). Easy, i tought, it's only the jetting. Thing i've noticed was little backfire on decel too. Soo rich and lean at the same time, crazy. I decided to put in 50 pilot (48 stock) didn't do anything. Ha ha i said too myself, misunderstood lean and rich symp. Then i've put 42 pilot...didn't do anything either. I've put back the 48 pilot as everyone run with, but try to lower the needle. (on the 3nd notch instead of 4, on the stock needle) Didn't do anything. Then after hour of tried to get that search fonction working in TT forum. Some people disconnect the TPS. i dont like the idea but i've done it of course. That helped the 1/8 sputter but not that much, and backfire was stronger. Then, the carb must be dirty came out. Soo i decided to take off the carb and started with the slider section... it was dirty! little black kind of old sticky dirt. Cleaned it and used some pressure air on every jet, i didn't forget the pilot one! Didn't do anything. Even at idle the motor seems to sputter a little , like if the choke wasn't fully seated. i've checked the choke assembly and nothing special came out. It seems to block the hole correctly. Checked the mixture screw too, it still there in the hole at 1-1/2 turns out. I have an FmF ti-4 pipe, stock air box, lid on (for the battery) and everything around that is stock. Temp is around 75, 0 altitude, not much of humidity. Maybe WR and i just dont belong together! i ride at 1/8 steady lot's of time, in those slow technical trail, so i need an 1/8 throttle!! I've looked for an leak somewhere, but i've double checked all the connections...there is no leak. And i even sealed a section in the air box where dirt could get in. I am gonna put back the stock exhaust to see if it can be better. I really need help again. Never been that lost with those new 4 strokes.