I have a 1983 GMC Sierra 1/2 ton long bed with 53,000 original miles on a 305(H) engine that needs some tlc. I just drove it from Portland Oregon to Phx Az where i live now knowing the carb needed rebuilt before I left... Well I can't avoid fixing anymore since the secondary "butterfly/bowl" (called??) won't open at all during driving condition.. The trucks backfiring on accell and just running bad.. It will run fine if I wedge the back butterfly open but I can't really do that and drive it around.. So I'm wondering if there's a bolt on carb that I can but or would it be better to rebuild the one I have? I've replaced some vac lines in hopes i just had a leak but it did nothing for it..