EFI return line, use emissions return?

Well, everything is relative.. and I did find that the ols cannister vent line to the engine compartment was for all purpose and intent blocked by internal corrosion. (no kidding!)
So had my fioller cap not been vented, I would probably have sucked the petrol tank flat a good while ago.

Obviously, since fuel is being sucked to the mechanical pump on the engine, there will inevitably be some pressure drop as a function of the flow VS cross section of the tubing. But I doubt that this is low enough to change the boiling point of the fuel significantly.

Anyway, I did install a new copper return line, ID 8mm, and now everything seems to work just fine, hopefully it will continue to do so when sumer comes with warmer weather! :)