Dual tanks/Switch valve/Return line Questions

Sorry if this is been answered somewhere, I have been reading through all of the posts and there is lots of good info but nothing really answers my question. I have a '70 CJ. It has a 283 Chevrolet in it, running a 2G carb and a mechanical pump. I will be running the stock underseat tank which has a vented cap I believe. I will also be running a tank out of a '88 Wrangler so my fills are both on the driver side. The wrangler tank has a non-vented cap I think but the tank has the two small nipples on the passenger side opposite the fill which may be for a vent? It also has the vent line on the fuel side going up to the fuel filler. I want to run the one gauge and have a dash switch to switch over the tanks. Both sending units have a return on them for the fuel. All of the 6 way electric switches such as the U7001, I have found are made for an electric pump pushing from the tank to the valve. Will this type of switch work with a regular mechanical fuel pump? Has anyone used one without the electric pump? I would like to keep the mechanical pump on the engine instead of running an electric pump for each tank.
Or should I just do away with the return lines and use a 3 way electric switch? If so, which 3 way switch works with a mechanical pull type pump?
Will the non-vented cap, if that is what the '88 uses, work without a return line? I am a little confused if the small fittings, which look like about 5/16" are for venting or what they are for as well.
Sorry for all of the questions. One of these days I will start a build thread. Just have not had the time to post all of the pictures with my work schedule.
Rog

 

I don't have anything useful to add, but I'm interested in hearing other people's answers, as this is the same setup that I want to do on my Jeep.

 

I'll be heading to my local napa for the following:

using this vehicle: 1976 Dodge Powerwagon "Adventurer Club Cab" (heavy half-ton):
dual tank switch on the dash (made by standard IIRC)
dual tank switch solenoid (also made by standard IIRC).

I believe it's a 5-pole elec switch, and a dual-inlet and single outlet solenoid. If you keep your return lines, then you just need a second solenoid plumbed in reverse I think (posimoto described something like this somewhere).

Elec switch carries the on-off for the solenoid and then swaps the wiring from the tank sending units to the gauge on the dash, and has common power (I don't remember, been since '90 since I had that old power-wagon).

Only other thing I did was plumbed an elec fuel pump with a toggle switch on the dash on the motor side of the 'from tank' solenoid, if the manual pump didn't want to do it's job (on occasion, it helped, especially if you drain one tank to re-prime the line). If you do the elec fuel pump, you may need a pressure reducer.

I'll be doing the same on mine.

 

Danefraz, thanks for the information!! I appreciate it.

 

The fuel return line is actually the issue. They make manual and electric valves that have the fuel and return systems you can plumb in.
My 3B is easy with the 2 underseat tanks, no return lines.
A friend put an aux tank in his work truck with the simple valve. He smelled gas, fuel leaking out of the stock tank neck. Being a typical GA boy, run the stock tank until it is almost empty then switch to the aux tank and let the return line fill the stock tank.
One time he lost a throttle return spring on this truck. Find an aspen branch, use your belt to hook it to one of the braces under the hood and use a boot lace to hook to where it is needed. Yeah, he is a VW fanatic.

 

http://www.earlycj5.net/forums/showthread.php?67359-Posi-s-Do-over/page18&highlight=switch+valve
Look at page #18 post #172 and page #24 post #231. I'm using this with my manual fuel pump.
Look at Posimoto's build. I did the same with my 2 tanks and it works great. I mounted an electric switch on the dash and when I flip it over to a tank, it not only switches the tank but the gas gauge works as intended. I cant remember off top of my head but I believe the valves came from Tom's Bronco Parts.
http://www.tomsbroncoparts.com/AdvancedSearch.do
The 2 fittings coming from your back tank are probably for smog on the newer JEEP, (roll over valve).

 

Rozcoking23, thanks for pointing me in the right direction! So you have these two valves mounted on the frame, one feeding from the dual tanks to the switch then to the manual pump on the engine and then the other switch as a return? That sound like exactly what I need to do.

 

Yes. Both are mounted on frame. The first valve is for feeding the manual pump. The second valve is for the return lines. I wired the valves together so when I flip switch it runs both valves. The directions for the switch tell you how to wire so the fuel gauge works on both tanks.

 

I had dual tanks on my 80 series Landcruiser. It was set up with a single fill pipe with a plunger cut-off to select which tank received fuel. This might be possible for you. We made PARALLEL fuel systems with fuel level senders in both tanks. Installed a valve in the engine compartment and a circuit that allowed us to switch tanks from a switch on the dash that also selected fuel gauge input from the fuel sensor in the tank currently selected. Ran a frame mounted filter with dual input/output and non-return ball valves.

I could carry up to 69 gallons of fuel and had a range of about 800 miles. It was awesome for the kind of exploring/hunting/camping trips I do in the Western deserts.