Fuel Tank Questions

[Jayschevy]

I have a few questions about the stock gas tank that's in the cab of my 71. I think I know but I need to know for sure which lines from the tank are the supply line and which one is the return line.
I'm guessing that the line coming out the top of the tank is the supply line, correct?
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Also am I correct to say that the line coming from the outside running alone the bottom of the tank is the return line? If so, this line runs up the passinger side of the back window and another line runs to the tank. Where does it go?
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I just need to make sure that I know for sure which lines are the supply and return lines because I'm planning on taking the tank out of the cab and putting a Boyd tank in the rear.

[71meangreenc10]

Its a vent line from the charcoal cannister.

Smitty

[Jayschevy]

So is the vent line a return line? And is the supply line coming from the top of the tank (sending unit)?

[1969K10]

no return line. the fumes from the charcoal canister are vented back to the fuel tank.

[68gmsee]

You are correct. The line coming out of the top of the tank is supply line to the fuel pump.

I'm not familiar with the other lines but as mentioned more than likely just vent lines for the tank. However, you say one line runs up the passenger side of the back window. Where does it connect to the tank from there? The vent lines I'm familiar with are doubled up with the sending unit supply line.

If I had to guess, someone replaced the sending unit and used a non vented unit instead of the vented one.

[Jayschevy]

The gas line running up the side of the tank comes from under the truck. It doesn't come from the tank so I'm sure it's not a vent line. I'm using a self venting gas cap.

[Jayschevy]

Anyone?

[LT102]

I just pulled the tank on my 71' C20 and there was only one line, the one running to the top of the tank where the sending unit wire attaches. I will get the Assembly Manual out and see if these lines are shown. Got my curiosity going.

[Jayschevy]

Originally Posted by LT102

I just pulled the tank on my 71' C20 and there was only one line, the one running to the top of the tank where the sending unit wire attaches. I will get the Assembly Manual out and see if these lines are shown. Got my curiosity going.

The second line came from under the truck trough the floor. It runs along the bottom of the tank than up the side of the window on the passinger side. Than it runs into the top side of the tank. I'm guessing it's a return line.

[ChevyCruizer]

The lines that do up into the cab will come out easily if you want to look at them. They just go up about a foot and then do a 180 and hook back up to them self. Understand?

Not all trucks have a return line. Look at your fuel pump, if it has 2 ports then no return line. If it has 3 (usually 1 is smaller) then it has a return line.

In the picture in post 1, that pickup is not for a return line system. If it was it would have a 2nd port and that would be where the return would go. I can get a pict of a very rusty pickup that has the second port once I get home.

Thanks, John

[cdowns]

it looks to me as you do not have the original 71 c10 gas tank
the original 71 c10 had the one supply line from the sender and then another line from the top passenger side of the tank that ran up the door frame into a high loop to prevent siphoning then down thru floor up to charcoal cannister to carb // and that roundabout system was your tank vent/// the 71c10 gastank didnot have a vented gascap

c20 did not have that vent

[Leftlane]

My original '71 tank is the same as yours.
1 fuel feed line, 1 vent loop up the B-pillar to the canister.
No return.
350 th350 factory A/C.
Posted via Mobile Device

[68gmsee]

Since you're going to remove the tank and move it to the rear, just get rid of all the extra lines. It's not going to be stock anyway.

Just follow the line from the sending unit to bottom of truck and to the frame to fuel pump. That's the one you will be using. If you are going to use the mechanical pump on the block and you have the one with three lines on it, get one with just the two lines, inlet and out to carb. Their fairly cheap.

[ChevyCruizer]

As promised here are the pictures. First one shown the outside of the tank sender unit with the 2nd return line. The second shows the inside so you can see what it does.

Told you it was crusty. LOL

I agree with the other comment, just run a feed line and dont worry about the other hoses. Just make sure your fuel pump (if using an engine mounted) only has the two ports like I mentioned above.