so i have a 2008 400ex. ive never really had any problems with it but lately its been tough to start. i dont really know how to explain it but it wont idle without the choke and bogs/cuts out when i give it a little throttle to keep it running, once it gets warmed up it runs fine and will idle good if i turn to the left so its giving it just a little bit of throttle. but with the wheels straight it idles low and will die. the chain came off a while ago so it was sitting for a little while (maybe 3 weeks.. maybe longer im not sure) it was smoking but im pretty sure it was just carbon build up. i changed the spark plug and have been riding it a little bit and the smoke has gone away. i was thinking maybe the carb needs cleaned? maybe bigger jets? as far as i know its 100% stock. oh one more thing, the air filter was very dirty. i cleaned it the best i could but i plan on replacing it soon. maybe thats the problem?