The only problems I have had on my cars myself are starting and running after a hot soak. My Pierce is not driving yet so I am trying to decide on an insurance system to install before the hood, fenders and runningboards go on making it much harder to to install. It could be I won’t need it but my tests so far indicate it is likely to be a problem. There are a couple basic ways I am aware for a recirculation bypass system, one is to just use an orifice at the carb inlet for the return line to bleed a fraction continuously of the basic mechanical fuel pump feed back to the tank to keep more circulation going through the pump and lines. This diverts some of the mechanical’s output unless an electric is boosting it.
I am thinking of a system,that uses the large excess of a rotary electric pump to recirculate only before and after briefly to cool the system and purge vapor after a hot soak. Most of the time it will operate normally on the mechanical without recirculation. It would be more effective as needed also for driving vapor lock. My original question was directed at trying to decide what a maximum pressure should be with the electric engaged. I think the answer is probably 1psi or so to make sure the electric doesn’t overwhelm the float valve in a hot carburetor and start overflowing.