My Mono-jet carb (1970 Rochester) can set for three or four weeks and still fire off in just a few cranks and couple of pumps, not sure why a Model B would be any different. Sounds like a vent issue or casting issue. Fuel sure isn't going to siphon out the needle and seat clear back to the tank.
I would rebuild the carb before installing a electric pump. And if you use the electric pump, be sure to use a momentary push button only or wire in a safety switch to the oil pressure if using the pump full time. NEVER EVER use a on/off switch with out a safety backup, Never.
