If you go to an electric fuel pump, wire it to the IGN circuit only. It's tempting to wire the pump to both the IGN and START circuits. However, wiring it to both creates the potential for the START circuit to be partially or fully energized when the ignition (key) switch is in the IGN position. (While electricity tends to choose the easiest path, it also "wants" to go everywhere it can -- anything and everything that leads back to the negative battery or alternator terminal.)
Wiring it exclusively to the IGN circuit means the pump would not be energized when the ignition switch is in the START position. So, you'd be relying on fuel stored in the carburetor float bowls. (This is the situation anyhow with mechanical engine-driven fuel pumps.). This means your starter and ignition systems needs to be in top condition to ensure a quick start. The battery and battery cable also need to be in top condition, for this reason as well as other reasons.
In the case of a AFB hot soak, I'd recommend a separate momentary (pushbutton or spring-loaded toggle) switch. With the ignition key on the OFF position, pressing and holding the momentary switch would provide a separate circuit to the electric fuel pump, allowing the pump to 'prime' the fuel system and refill/top-off the carburetor float bowls.
This set-up would also be useful in hard to start engines. (Mostly big blocks -- 383, 413, and 440 cu. in.). If the engine doesn't fire up in less than a minute of cranking, you could turn off the key switch, press and hold the momentary switch to 're-prime' the fuel system, and then try again to start the engine.
You might even find the momentary switch useful as part of your normal starting procedure. i.e., press and hold the 'prime' switch for 5-10 seconds before trying to start the engine, to ensure the engine has adequate fuel.
If this description is confusing, let me know. Normally, I'd provide a circuit segment diagram but computer problems prevent me from creating a diagram at this time. (I hope to have my computer fully operation by early next week.)
Eric - this plays into your dual fuel (propane and gasoline) conversion. I don't want to discuss it here because your efforts are relatively unique. PM or email me when you're ready to discuss it.
