fuel line question

[jetboy]

While at the local 02 salvage place, I noticed that the (plastic) fuel delivery line for a later (75) model car was a larger diameter than the line in my '70 model. I also noticed that my 70 does not have a metal fuel return line of any sort-

what is that fuel return for anyway(just a cali smog thing?), and if I am running a larger carb than the original solex on my 70, will the larger diameter fuel line help create a smoother flow? or does it really matter?

-j

[2002]

The plastic line running through the cabin is the main fuel feed to the filter then to the fuel pump on later models. The metal line on the bottom of the car is the return line. The return line was designed in on later versions to prevent vapor lock.