yes fuel will be evaporating, but if you still get a few shots after a couple days, the problem is fine tuning, and as Grigg points out, technique - a small block should fire on the first or 2nd rev, could be the timing is a bit off or the plugs are fouling ot your frenetic pedal pumping is flooding it
has it always been this way? have you done an ignition tune since you got it back on the road? HEI or points? how much do you drive it? long trips or short?
Bill