Why isn’t fuel going to the carb?

james m smith said
return line to prevent vapor lock by letting fuel always circulate rather than just sit there and get hot, orficed nipple

When did these come about, I grew up driving late 60's 70s cars never seen it. Now if it was on later 70's cars I may have never seen it. never owned late 70's Mopars. Anyway, did the OP figure this out? I thought he got it running