Occasionally my truck has trouble starting (85 carburated ranger) and it struggles for a couple of minutes.?

sometimes you have to put the gas to the floor and then crank it for 20 seconds or so, when it does go it studders and runs really ruff at a really low RPM, then after a minute or 2 it will all of a sudden come to life. Is this the fuel pump? or maybe electrical? I dunno.