Carburetor loses prime after 8+ hours

Good chance you're looking at either installing a Carb kit or an electric fuel pump to solve your problem. I' ve been doing it the hard way for the 32 years I've owned my Duster....when I get tired of priming the carb manually (pouring gas in)because the gaskets and seals are no longer performing their function I buy a carb kit and a case of beer and go over the rebuild again with someone who's more proficient...I enjoy the process...an electric fuel pump is a good idea...do both and be good to go for awhile.