My van was sputering and then today it quit running and then I let it set and it stated. I went to go again and it back fired and won't start again...It's like its getting way to much gas or it's not burning it all right! Can anyone help? Thanks Danno

Optional Information:
1989 Chevrolet chevy van 350 auto

Already Tried:
checked all the spark plug wires,checked distribator,took off air cleaner to see alot of gas!