If the pressure from the purge line and the air pressure line are roughly the same, could we not just hook the purge line directly to the tank and call it done? No fuel pump, no extra check valves, y fittings, etc? That would by far be the simplest solution.
The questions left to answer there would be, would the pressure be adequate regardless of RPM, and the amount of fuel being dispensed? I would want to test it at idle, at WOT, when it’s hot outside, when it’s cold, etc, just to make sure it would be reliable.
The next thought I had would be if the purge line did not provide adequate pressure, perhaps could we use a fuel shutoff valve on the air pressure line to control the amount of additional pressure added to a “y fitting”?
I’m talking about adding something like this pictured below, and crack it just enough to make sure there is enough pressure in the tank to push gas into the carburetor, but not so much as to block the check valve from the purge line.
Something like this:
I find all of this very interesting, and I intend to try this, but unfortunately not any time soon. I put my boat away into storage this last weekend, and promised my better half that I would work on other projects for the foreseeable future. After the weather warms up in the Spring and I pull the boat back out, I can report back.