I just bought a 2000 WR 400 used and is in good shape. However, I might have some carb problems. It starts right up with the choke but will not run once the choke is put back in. Even after the bike has completely warmed up (hot) after running several minutes with the choke on it doesn't want to sit and idle. It just doesn't want to run good until it has been ridden around for a while. After it has been ridden for a while it runs fine. Tried the idle adjustment to no avail. Any suggestions?