Possible marginal wiring to ignition coil, anywhere from ignition switch thru any connectors, ballast to the coil. If any point along the way you have corrosion, marginal connectors, stranded wire compromised, you will have much higher resistance, thereby lessening the voltage the coil will see. Engine may still run but not well,,,particularly at idle.

Run a jumper from battery to plus side of coil bypassing all these potential issues for a quick 5 minute test. Best to disconnect existing plus wire on coil while running this test.

Not ruling out bad fuel or compromised carb however, particularly as car been sitting for quite some time.