Adding a return tunnel fuel line

[boxer246]

I'm getting ready to do some work in the tunnel of my car (70 T)...shift bushings, throttle cable bushings, speedo cable etc. I'll be taking the seats out for easier access and the shifter, E-brake and tunnel cover off. How difficult will it be for me to add a second (return) fuel line through the tunnel? Better to thread it through from the front or from the rear? Reason is Im considering building a MFI engine, but even if I decide not to I do like the idea of a return fuel line so I can use a PMO fuel pressure regulator with the Webers. I've never really liked the idea of the deadhead fuel delivery system. Also, is the stock hard return line on the MFI cars the same size as the supply line? Is it 8 or 9mm?

[Matt at Pelican Parts]

Some quick searching on the forums shows that various people have run the return line through the tunnel. There are a few threads where people discuss making their own.
This one has a user who made same from polyamid:
https://forums.pelicanparts.com/porsche-911-technical-forum/683644-fuel-return-line-install-suggestions.html

And another one here discusses the use of 10mm line:
https://forums.pelicanparts.com/porsche-911-technical-forum/989245-anyone-run-10mm-return-fuel-line-74-75-cis.html

As far as the best way to do it i am unsure. hopefully one of our experienced members could answer that for you.

Best of luck!
-Matt

[Uwon]

First unwind your new fuel return line at room temperature and let it straighten out.
Run a relatively pliable wire from back to front inside the old line. You need lots of slack on both ends, especially at the rear which needs at least 1 1/2 times the length of the return gas line.
You should fold over the starting end so it does not jab against the inside wall.
Tie the wire at the front using one of the front gas tank hold down bracket holes.
Pull the old line out from the rear.
Check that the new line is the same length as the old one.Then fold the wire rear end.
Get the wire as straight as possible.
Feed the rear end of the wire into the front end of the new gas line.
Guide , prod and turn the gas line as you feed it to prevent getting stuck inside the tunnel cavities.
Keep the wire reasonably taught as it will help guide the gas line. A third hand is useful at this stage to keep the wire relatively taught.
Bingo, you are done!
Cheers,
Johan

[BoxsterGT]

Excellent tips from Johan.

I may be repeating what Johan has said, but it might help a bit.

When fitting a new "Second" Tunnel line in a 911 that never had one, it's most important you have a helper here to push/pull, either at the front or at the rear.

Once we have made new holes front and rear for the 2nd line, we use Nylon weed trimmer line that is pushed up inside the original steel tunnel line with double the extra length as above.

We would then secure the weed trimmer line at the front pan/bumper area and pull the original steel line back out through the tunnel as far as the shift coupler. Run the 2nd line through it's new hole and attach to the Original (access inside) with tape.

Taper this so you have a smooth joint and can pull the pair as far as possible to the front without snagging on things inside.

When at the front, remove the tape (up by the pedals) and feed the 2nd line through it's own hole and proceed to connect your front and rear hoses. Usually the tunnel lines have enough extra length to move back & forth to get everything comfortable.

Next is to insert the grommets using a little lube and last is to bend back the tabs over the lines to secure them in place.

Hope this helps.

Len

[Uwon]

Len,
Interesting that do not have a second hole front nd back. My early ‘71 T with matching motor also has Webbers and has the second line holes which look to have been punched out by the factory. I’ll have to have a closer look.
Johan