07' Yamaha Big Bear irratic idle 400

Just adjusted valves on the Big Bear, and put new plug in and new diaphrame needle, needle seat, and choke, and really ever since we have had it it has had irratic idle, it almost surges best describes it. Idles fine then drops then speeds up say you hit throttle it takes a few seconds to idle back down to idle position, What else can be done with this stupid thing. They are putting all this crap on these bikes carb warmer, just give them carbs and none of this other BS crap and it wouldn't so difficult to work on.