Fuel plumbing problems

[dlampe]

I am sorting out my GT40 fuel system. With 2 tanks there is a lot of ways to get confused. What I want to do is run from the tank to the filter to the pump to the regulator(s?) to the carbs (weber's) then back to the tank. The problem I am having is how to run a return line back to the tank I am pumping the fuel out of. I can control which pump is on by a switch on the dash. When one tank is empty, hit the switch, go to the next tank. The left system and the right system come together to feed the carbs then the excess fuel needs to go back to the same tank it came from. Any ideas? Do holley eletric pumps have check valves? How do I plumb this system?

[Anthony]

Buy one of those electronic valve, gas tank selection valves, ones pick-ups use, and run a single return line, then have the valve activated by the fuel pump switch to direct flow back to the correct tank.

[dlampe]

Thats a great idea! any idea which trucks have that switch? Or where to by it? Probably from the dealer.

[Anthony]

Originally Posted by dlampe

Thats a great idea! any idea which trucks have that switch? Or where to by it?

http://www.jcwhitney.com/autoparts/P...wflag=1#review

[trularin]

The return line is usually on top of the tank, why not Tee the return line fittings and let the return fuel go to both?

Just a thought.

[Blittleton]

dlampe,

Why don't you run from both tanks at the same time and then return with a t-fitting to both tanks. No additional switches to deal with.

Bill

[Clois Harlan]

My thoughts exactly. Why would you want to split of from each tank just to have to have another switch on the dash. If you run a feed line from both tanks to a Tee and then up to your fuel filter and then pump then you only need one fuel gauge. The return lines could actually return in the same fashion since by doing your plumbing this way you should have equal pressure on each tank at all times. By running a single fuel line with a outlet line running between them you (in theory) should be able to maintain the same fuel level in each tank. Given that scenario you could get away with a single return line to which ever tank you want.


Clois

[strictlypersonl]

If there is a significant difference between tank return flows (not to mention tank pickup flows), there is the possibility of overflowing one tank.

[767Jockey]

Couldn't this be solved by putting valves in each return line to allow you to "trim" the return flow over the first few tankfulls? In other words, leave both return line valves fully opened. If you find that the left tank fills a bit more quickly than the right, you would just tweak the valve in the left tank closed just a hair. Over the first few tankfulls you could get this setting perfected, and after that point it really shouldn't change much, no? Just an idea.

[dlampe]

I like the electric valve idea best. The switch that activates the pump can be tired to the valve also. That seems to be the simplest solution. (at least to me) This is why I love this forum. Great responses, fast!

Thanks guys. This is just the beginning!

[Commander]

Big Jaguars have used dual tank setups for decades. From a Jag helpsite:

Fuel Plumbing.

D Jetronic introduced the recirculating fuel system used on just about every electronic system since until the recent advent of non-recirculating systems. The pump draws fuel from the tank and delivers it to the fuel rail(s) (the pipe which feeds the injectors) having an exit to a pressure regulator which maintains constant pressure at the injectors and spills excess fuel into a return pipe to the fuel tank. The flow rate in the system is always in excess of the maximum that could ever be required by the engine. D Jetronic regulators are adjustable but should be set to the correct pressure.

The V12 installation uses separate fuel rails and regulators for each cylinder bank but the two are linked and it is important for both of the regulators to be correctly adjusted so that the slightest backing-off on either will immediately cause a pressure reduction. Twin tanks in XJ12 saloons have a system of solenoid valves controlled via the tank selector switch to direct recirculating fuel to the tank from which it originated. Any air entering the system when a tank runs out is purged by a bleed valve located in the spare wheel well.

There is a non-return valve built into the pump, and another attached to the air bleed unit on saloons, which are intended to retain pressure in the rails after switching off with the intention of preventing vapour lock during a hot restart. Unfortunately this can still happen, partly because of the relatively low fuel pressure, and was a minor irritation associated with the D Jetronic system.

On saloons the solenoid operated change-over valves, which ensure fuel is drawn from, and returned to, the selected tank, can fail, leaving one tank unselectable or rapidly draining one tank into the other. If the tanks are more than half full in total, after filling one tank the remainder will be ejected through the vent system. Fortunately the valves are easy to change, later cars having a separate return valve to each tank in the rear wheel arches, earlier cars having a single three way valve in the boot well, along with the three way selection valve.

So there are parts available from Jaguar service centers to do exactly what you want to do. The question is, do you want Jaguar electronics in your car?

[dlampe]

Do holley electric pumps have some sort of check valve in them to prevent reverse flow?

[767Jockey]

Originally Posted by Commander

So there are parts available from Jaguar service centers to do exactly what you want to do. The question is, do you want Jaguar electronics in your car?

They don't call him "Joseph Lucas, Prince of Darkness" without good reason!

[trularin]

Mine does, I think they all do, but that doesn't mean there will residual pressure at the carb.

It is a white plastic piece with a spring, well, at least mine is.

[Morris]

Dean

Do you know where the pick-ups are inside of your fuel tanks?????

If not ....you better find that out first...... then we can figure out how you want to get the fuel up to the front......

An additional sump tank may be the better way.....

Morris