Stop in for a cup of coffee

OK. Plunger type pump. The inlet for the accel pump is relatively high. If the fuel in the bowl is low, the inlet is exposed to air. Worse if the seal on the plunger isn't.
Tapping it shouldn't do a damn thing unless there is so much varnish from old fuel drying that stuff is sticking badly.

Fill the bowl the way Ben Drinkin suggests.
And Mike is right about today's fuel. A higher percentage of it will vaporize at lower temperatures than when these cars were new. It varies from winter to summer and state to state and even within state but its all crappy, just some is crappier. Winter fuel is always worse, with higher vapor pressure allowances.
Funny, My AFB on my 66 the fuel would evaporate over night. In the Holley on my 69, it seemed to never evaporate..