6 vs. 8mm gas tank feed tube for Webers

[Shaun 69 E]

I just had my gas tank professionally cleaned and resealed as step one to rebuilding the fuel system on my 73 with a 69T motor with Webers. A new fuel pump will be moved up front instead of under the left rear seat. have a basic "big metal dial" type fuel pressure regulator.

PET says to use a 6mm tank feed for T (carb'd) cars while E and S with MFI get the 8. I have a new 6 and a very good 8.

Does it really matter which one is used? And why?

[rick2]

Hey Shaun, I'm no expert and I'm making a couple of assumptions here but I'm guessing you are going to use an after market pump? The Purolator aftermarket thumper pump comes with a variety of nipple sizes and I would match the size to which ever tank feed. That way you have the same size hose. I would go larger so it doesn't stress the pump as much. Not sure why you are moving the pump since there isn't much room up front. My guess is that Porsche used the bigger feed for MFI due to the higher pressure and volume. I prefer the stock MFI pumps and they generally put out 12 psi and I've seen from 9 to 15. What you need to be more concerned with is your output. Four is good and 6 being too high. I used the Purolator adjustable regulator and it sucked. The most it limited a 12 psi MFI pump was 3 psi to get 9psi which is way to strong for carbs. I ended up using the Holly one from Summit. You'll want a larger line coming out of the pump so the line doesn't kick up the pressure. Make sure you have a return line so pressure doesn't build. Hope any of this helps. I may have a pic if it helps as well.

[edmayo]

The larger fitting is the suction line (ie. feed line) to the fuel pump. From the outlet nipples of the pump a smaller line is used on the pressure side up to the fuel filter and the injection pump.

[MarkS]

Shaun, ditch the "big metal dial" regulator. I have personally seen two of them fail resulting in fuel leaks, one on my car. Get a regulator with a guage and set it to 3 PSI.

[Shaun 69 E]

Thanks guys, Rick, you are absolutely correct RE: feed tube size.

yesterday I took the day off and installed the newly dipped and recoated (though ugly) fuel tank with the 6mm feed and I welded the banjo closed, tank-body foam seal from Home Depot. Reworked the rear fuel lines from tunnel up to Webers and am waiting for a PMO regulator to arrive on Monday, same time as the vintage used pump coming in. Also ran a 14 gauge factory wire (stripped from center tunnel spare harness and sheathed in factory tubing originally running to the right rear taillight) from fuse #5 into the smuggler's box and down to the crossmember.

definitely one of my better installs and the car should run for more than 4 blocks at a time after it's completed Monday/Tuesday.

Question on fuel filters. I've seen one filter before the regulator and 2 filters just after the regulator. Given I have a brand new system, do you think 1 filter before will be sufficient? I like the idea of unrestricted lines running from the regulatory to each carb.