I think you are talking about the "vapor return line". This is not a great definition since the return line comes off the fuel pump, and while it does return vapor to the tank if there is any, it's just as much of a fuel return line that allows some fuel to recirculate back to the tank. This is a good thing to have, and might keep you from sitting alongside the road on a hot day in traffic. It's not really part of the smog system at all.
To confirm this, just look at the old mechanical fuel pump. It should have a 5/16" intake and a 1/4" return on it. The return is actually reduced down to about .063" inside the fuel pump which limits the amount of fuel that is recycled.
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Mick Batson
1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 Catalina Safari Wagon.
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