Both of the fuel fillers on 1974 S2 have a vent line that runs up somewhere near the base of the rear windscreen. I can't tell where it goes or what it connects to and my searches haven't shed much light. Does anyone know where these go?

 

That's part of the evap system and my most dreaded part of these cars. Tubing that loops in the C pillars taking fumes up to the evap canister in the right front wheel well. I've had raw fuel all the way to the front wheel well on too many occasions and fumes in the interior. On my XJc I recently bypassed the whole thing and ran fuel tank vents to the ground as was done in the UK.
Btw... You have to remove the rear parcel shelf and rearmost trim, and pull back the rear cantrail trim to view the tubing. I left them in place. Not much you can do to them and the hose connections are normally accessible after removing the fuel tanks. But I think I changed them once by removing the tubing inside the car. Better to pull the tanks. If you can pull a quarter inch of extra hose through the filler cap well, you could cut off the dried up end and re-connect if that's your issue.

 

Thank you @slofut . The ends of the hoses are dry-rotted and I wanted to replace the hose but could never find where the other end landed. This is very helpful.

 

I agree with Slofut.
I chased a constant fuel smell in a Series 2 and eventually just vented the tanks to overboard.
That stopped it!

 

^^^
That's what they did with mine at the time of conversion.
They had to leave the canister and all its hoses to satisfy the SMOG cops but they don't go anywhere.
(';')