how long has the car sat before you started driving it? using todays gas has ethonal in it which is not a bad thing but it is hell on old cars. had the same trouble with the studebaker lark i bought last month.i dropped the entire fuel system and replaced the lines with stainless steet and neopryem hose had the tank flushed out and sealed for today gas. the ethonal cleanes the fuel system and all that varnish has got to go somewhere,also remove the pump and check the dia. in the pump,if its a rebuildable tpye.the ethonal will soften the dia. it may look good but replace it.that is were i would start.good luck.i'd stay away from sbc.don't like them