Chevy 305 is roaring though the carb when you give it gas, and throttles like a boat (slow rev climb)?

what could i do to fix this and what the heck is going on here? iv never heard an engine make that horrible sound before. im not very well versed in small block Chevy, please help! p.s. set the timing perfect with a timing light and even went to a shop to make sure the timing was perfect. still no dice.