my 1999 wr 400 was running fine during my last ride, i brought it home and changed the oil. then went to go for a ride in the desert a bit higher altitude and it was rainy that day. anyhow the bike fired 1st kick but when i turned the choke off it would not idle it has always ran great at this location before the bike seemed to run normal except for the no idle condition, what would cause this overnight change, i know its probably the carb but which part. i am no carb expert i could work on 2 stroke carbs but 4 stroke carbs look kind of scary. ps when i got home the same symptoms were still present no idle without choke on. is it the air screw, idle jet, or acc pump?