I have a gen6 502 mag mpi that has been converted to a carb 540. The raw water pump doesn’t have a fuel pump boss and with the alternator placement, too many brackets would have to be replaced. So I am looking at electric pumps. Either way , I am planning on running a return line to the filler neck as I want to avoid vapor lock and give greater pump longevity. The Weldon a600 to a bypass and then to a regulator is what I have spent some time looking into. The a600 is not uscg approved but I would feel comfortable using it. Thx in advance

A carb will not vapor lock

I had a 1975 international scout. 345 4 speed. It begs to differ !

Last summer I was getting a lean stumble at mid rpms after a few minutes steady speed.
When it happened the AFR would shoot up, and If I throttled back or if it stalled, it would have normal air/ fuel on restart.

I decided to err on the side of caution and plumbed a return fuel system last fall. Kept my Holley Blue Marine pump and opened everything that was undersized to 3/8" ID.
Then in the last few weeks I realized it could have been timing related. I checked my timing in the spring, yup too high. So I set it back to a normal #.

BTW CPPerformance has the return bung setup for your fuel. I started out to make one and found that I would have spent a lot of time and money cause I could not fab up and weld things as I wished

Haven't gone for a ride yet, but she's almost done getting shiny in the yard!

And I have experienced vapor lock on old beat up 1960's American luxo barges when I was a young driver in the early 70's.

I’m using a Weldon A600 and it’s an impressive little unit and super quiet compared to the Holley pump that came with my boat. I put rubber boots over the terminals with dialectic grease as it otherwise seems to be sealed up pretty solid. I can’t speak to the legality of it not being a USCG approved unit but I’m a fan of it. Jeff Harris uses Weldon pumps on his builds.

I ended up running a return line and also picked up the Weldon A600 pump along with their return regulator. I do have 3/8 fuel line , about 4 feet running into a fst fuel water separator and then 1/2 inch for the rest. My return line is also 3/8 running back into the fuel fill.