Won't idle, backfires when decelerating
2004 Sportsman 700 Hard to start, takes full choke and then 3/4 choke to keep it running. Idles at 1750, backfires upon deceleration when hot and will run well after acceleration begins but runs rough until 5 MPH. I removed plugs, L one was wet with gas. This ATV has 50 hrs and actually belonged to a little old lady who drove it to a mailbox and got too old to get on it. Someone, did not care for it and it had mud in the aircleaner box, and signs of being run through soupy mud everywhere, never had oil or aircleaner changed.Any thoughts would be appreciated.