Lots of simple reasons, takes time to test. Like Tim said, it's not vapor lock unless you have wrapped your gas line around the exhaust manifold. I will say your day time temps are higher than I thought.
Some possibles:
1. Gas cap not venting
2. Fuel pump
3. Clog in lines, tank pick up, hoses, filters
4. Carb needle valve, float setting
5. Vacuum leak in intake manifold, gasket, hose, tubing, connections/fittings
6. Gas level in tank was too low
7. Loose wire on dizzy, coil, ignition switch or faulty
8. Condenser and/or points
9. Do the easy checks above first, loosen cap, check filters, fill with gas, check vac and wires and report findings
10. Does sound like fuel delivery problem of the type that recovers. I.E. Gas cap, floating debris clog, pump suction. Just a guess. If it gets worse, that's a good thing. Hard to find intermittent.
11. Let's don't do any old man butt jokes.
