Is a return necessary in carb’d engine?
 

I’m replacing my tank, fuel pump and fuel lines.

Car was originally MFI, but converted to Webers by PO.

Do I need to (re)install a return, or can I just use a single line and a pump with the proper pressure for carbs?

Not necessary, just a good idea.

Something about preventing vapor lock. If you don't have a return line then I would probably just run it as is.

Lots of old cars with carbs did not have return lines. You would need a pressure regulator with a return outlet.

I was always told that carbs like cool fuel. A return helps that happen.

It also depends on the fuel pump you use. If you want to convert a CIS car and use the CIS fuel pump (or an EFI type fuel pump), you MUST have a return line or you will overpressure the system and overwork the pump. A fuel circuit without a return line is sometimes called deadhead arrangement. With that kind of setup, an inline fuel pressure regulator will limit the pressure to the carbs so they'd probably be fine, but upstream of the FPR, very high pressure would build, which is hard on the pump, and potentially dangerous. Pumps intended for carb fuel systems are often designed accommodate such a setup.

I agree with mepstein's comments, but honestly for a street car it may not matter much.

Send me a pm with your email I’ll send you some good reading on the subject.

My $0.02 - Back when I had (non-P) cars with carbs, I always made sure that a return line with a fuel regulator was installed. This prevented vapor lock on hot days and seemed to help the bowl fill valve last longer (or it also seemed that way to me). I also felt like I was fiddling with the carb less after the return lines went in.