sounds really rich. if the coldstart valve hangs ,that could do it, but I don't understand the clearing up w/ a new o2 sensor.I wouldn't think that there would be enough control range to compensate for a stuck coldstart without the engine runing really bad at idle.Has anyone turned the mix adjustment clockwise?The fuel distributor may be dumping at the plunger, into the air sensor housing . U could look in there w/ a flashlight after the engine runs a few seconds and see if it's wet. Becarful to take the cig out of your mouth while you're looking (G)