68 plymouth 273 question

i have a 68 valiant 273 2 barrell from factory ,guy i bought it from changed intake and carb to a edelbrock 4 barrel setup 600cfm carb ,i dont think he changed the cam. the car runs great but after driving it ,let it set ,go to start it, it crank over for a few befor it starts, could this be the carb setup or fuel pump leaking off ? would it be best to put the orginal intake setup back on it ? any ideals be helpfull