Accelerator pump or circuit problem...assuming the fuel pump is up to snuff.
Even if the gas evaps over a few days, it should still start after 10 seconds and stabbing at the throttle a few times.
I have an old '54 pickup with a single barrel flathead six in it and the check ball will stick in the accelerator pump well. Sometimes a few good taps with a hammer and away she goes. If it gets started every day or so, it works fine.