Dave - the length of time required for the bowl fuel to completely evaporate depends on several factors:
(1) type of carburetor
(2) type of engine ("V" or inline)
(3) to a certain extent, the ambient temperature
Aluminum bodied carburetors have greater evaporation
Carburetors with bowls directly above the throttle body have greater evaporation (a Carter AFB has much greater evaporation than a Holley 4150)
"V" engines (where the carb is directly above the "heat sink" a.k.a. engine) have greater evaporation than inline engines
Consider the Carter AFB; there are no plugs below the fuel line, and syphoning back through the fuel line is impossible.
I have two on my truck. If the engine is fully warmed up, the bowls will be empty 30 MINUES after shutdown.
After determining the issues, I modified the carbs to run with an electric pump, and I use the electric pump full time.
Jon
