I know tank to filter to pump to injection system.


What the hell is it, The larger port out of gas tank is the supply line?

Smaller port out of gas tank is return line?


My house has been having some LOUD conversations about this. I can not go forward til it is solved.


Signed Girlie Garage (lol)

Renee

From memory, bigger port is supply, and has a sock on the inside of the tank.

I don’t recall a difference in diameter at the tank.

Big port supply, small is return. As said before, supply has a filter inside the tank, the "sock"...

Having just done this (new tank, fittings all redone, new sock ) I used the same rubber line from both ports, same size.
They are the same size in the tunnel
They are the same size in the engine bay.

There is a size increase at the 75/76 fuel pump and filter, but it drops to the same diameter at the tunnel.

In older cars, it’s all the same size

maybe same size in a d-jet, definitely not same size in an L jet.
supply is larger. return is smaller.
have to check but memory says 9mm supply. 7mm return.
distinctly remember. built my own metal tunnel lines.
somewhere even have the old stainless end pieces with factory hose portions attached.
could measure them or look up PET.

It is a really good idea to open the tank and inspect that sock on anything over 15 years old.
If it's 50 years old, it's imperative in my book.

73’ 2.0L

They are two (2) different sizes. The supply line is the larger diameter and the return line is the smaller diameter. As others have stated, the supply line also has a mesh sock on the end of it inside the fuel tank which by this time be replaced/cleaned after 50 years.

pulled the box out in the garage.
for L jet.

supply 7mm Internal diam.
return 5mm internal diam.
(measuring the s s tunnel line ends that feed through firewall grommet).

Click to view attachment
Click to view attachment
Click to view attachment

engine bay the same two different sizes.
supply larger.

maybe D jet different. wouldn't know.
maybe 75 different too with pump in front.
these lines are from a 74.

They are the same. 74-75 is the changeover year.
Changed from the opaque material pictured to a black material & changed the lines to the same Dia. which corresponded to the move of the pump. So the material is spec'ed to withstand the pressure.

Run the larger line to the engine if you want to go fast and run the smaller line to the engine if you want to save gas

I just did new lines in my 74 and it has two sizes coming out of the tank. Larger is supply. I installed Tangerine Racing SS lines and he sells a reducer as part of the kit as the new SS tunnel lines are the same diameter.

Maybe this helps. Found here: https://bowlsby.net/914/Classic/TechNotebook.htm

Jeff that is SO nice....I have it all in my head but it's so good to have a drawing of it....Thanks for posting...you just always have the super cool info.....

looks like my in and outs
are not the same size

D Rex

One of my 914's has lg & sm lines in the tunnel and the tank. Two have 8mm lines in the tunnel and at the tank.

that diagram is fantastic. god is the details.

drove me back to take a closer look at the engine bay.
you would think i could have got that right in my info above about L jet.
given i put them in about 4 years ago. dementia.
both those lines are the same size in engine bay after FP as per mr b's D jet diagram.
the smaller diam.

all makes sense. its gravity feed non pressurised to the supply on the pump. you need the volume. for the original pump location.

pump in front a different kettle of fish.

Putting a two port pump up by the steering rack.

Early cars = fuel pump in engine bay. 10mm and 8mm. ( 3/8" and 5/16" )
Late cars = fuel pump in front under tank. 8mm and 8mm

Late cars have black nylon tubes thru the center tunnel as they can handle the pressure.
Early cars have clear (transparent yellow due to aging) and can't take pressure and are likely to crack due to age.

You can buy Stainless Steel tubes from Tangerine Racing $$$, make your own $$, or buy the black vinyl fuel line $$ (Dorman 800-071 25 Ft. Of 5/16 In. Nylon Fuel Line). You will want the 8mm (5/16).

Make sure to get E10/ethanol safe rubber hose like Gates Barricade. IIRC it's r13 grade. Low pressure hose is rated to 50 psi, which is more than our 36 psi, so it's good enough. The "FI" rated hose is rated to 225 psi and costs proportionately more. Use the proper FI hose clamps and not the cheap worm gear crap.