A speck of crap stuck in there, a sticky N/S, happens all the time. You probably have Moraine filters, which are just big tubes of brash mesh, at the fuel intake fittings on each bowl. They work pretty well in conjunction with another filter back along the line somewhere. I have mine back by the fuel tank. First just go ahead and replace the N/S and get the car running again. Then, over the winter, pop the fuel bowls off and inspect the bowls and metering blocks for crap,
zinc flaking, etc. Take out the Moraine filters and springs too and see if they've got any chunks of black rubber flecks or anything else in there.