need help with 89 chevy k3500
 

ok so this truck 89 chevy k3500 with the 454 has been sitting for a couple years now and i just started to mess with it. i got it running, kinda. but it back fires out of the intake well it did i adjusted the timming and now it just pop's when i rev it. i know the bad gass has a lot to do with it but im tired of chassin stuff if i dont half to so any help would be nice and i will let you know what i find the truck has over a 100k. any more ? you need to help me out just let me know. thanks