Mr.Duster

i was wondering if anyone can help me determine what would be wrong with my 340. i just put it all back together making sure the valves were seating and what not. it wont stay idling and it spits and spatters. my uncle has a diff. carb im going to try to see what that does for it, but do any of you think they might have the wrong cam in it?. i dont know what kind it is and forgot to take the measurements of it while i had the heads off and what not.