Dual Fuel tanks

I have a problem on my 68 cj5 that has me scratching my head. I am probably missing something simple. Perhaps someone has run into this before.

I have a 2 tank setup. The stock tank under the seat and a 2nd tank at the rear. There is a manual valve on the floor board just in front of the front tank that controls fuel flow. When I select the rear tank, the front tank would fill and eventually start to overflow. Then I would select the front tank until I needed more gas. Turn again to the rear tank, and the front tank would begin to fill again. I always thought this was strange, I checked the plumbing and it seems correct (althought the PO that did the install did a poor job on routing the lines). Both lines from the tank go to the valve and from the valve the line goes to the mechanical pump on the engine (V6).

Does this sound familiar?

Thanks,
Gary in San Clemente
68 CJ5, 225, T14, D18, OD
52 Wagon, F134, T90, S18

 

sounds like the fuel return line from the pump is still connected and returning fuel to the stock tank no matter which tank you draw from.
One option wopuld be to disconnect the fuel return line.
For ID purposes, the return line is typically smaller in diameter than the other lines, say 1/4" in diameter.

 

I agree, it sounds like the fuel return line. But I am curious, is the second tank physically higher than the stock tank located under the seat? If so, could the valve simply allow fuel to gravity drain into the original tank? It sounds strange, but I have heard of much stranger.

 

the changeover valve prevents siphoning, only draws on one tank at a time.

 

It's the return line for sure. My Jeep used to do that too. It would return the fuel to the rear tank no matter what tank it was being drawn from. I found a switch online that allows you to run a second return line so you have feed and return for each tank. I wanted to be able to isolate each tank and run them independently and not have them act like one big tank.

 

Thanks for the replies.
Sounds like it's the return line (or my switch valve is bad - unlikely).
My rear tank has no input for the return line so maybe I am out of luck.
I really don't understand the purpose of this return line?
If I block it off, will that put undue stress on my fuel pump?
Thanks.

 

My 225 doesn't have a return line... didn't when I got it, not saying someone didn't already block it off though.

 

That's kind've funny!

 

I have no return line either.

 

No extra stress on the fuel pump.
I don't use one on my flatty either.
Your choice, but the return line is over rated in my opinion.
I run in hot conditions...have had no problems with vapor lock or flooding in over 20 years.....

 

no return line here either. could change the fuel pump instead of blocking off the return.