I have a 350 I just bought recently off Craigslist and it ran great the first couple days! The third day towards the end it started backfiring in the airboxx and the exhaust tried to make it back but it died on me. I could get it to start after that but it would die soon after. I took the spark plug out and it was bad so I replaced it and it ran just fine after letting it run reved up a little. The very next day same thing happen but spark plug was fine. Now I can't get it to idle or it will just die. I adjust the air/fuel mixture screw and played with it a little and I could get it to run with the choke on and a little with just idle tried to adjust it a little more then it went back to how it was. Can't seem to find the perfect spot. Please help I've been google this for a couple days and can't seem to find a answer.