Hi All,
I’m having a fuel problem I hope you can help with.MY XJ6 is a SBC conversion, I’m having trouble getting fuel to prime my pumps. When I disconnect the fuel line from the tank to the pump the fuel will run from the tank but when I connect the line back to the pump the pump will not push the fuel forward. The pump primes then runs out of fuel and I can hear bubbling in the tank. The pump flow is hooked up correctly. I am using Holley red pumps and this is with both tanks. It’s as if the pump is sucking the line dry because when I again remove the line to the pump it takes a minute for the fuel to start running out of the tank again. Have any of you experienced this?


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1973 XJ6, 460Hp 357ci SBC, TH350 Trans, 2700 Stall converter

 

No immediate answer, but a few questions:

1. Was this a running set up, or is its new installation?

2. If you leave the fuel filler caps ajar so the tanks can vent are the symptoms the same? sounds a bit like you are creating a vacuum in the tank, if I am following the description.

3. How is this set up configured? dont understand why there are two pumps. Got a diagram?

 

Swap the wires around. Pump/s are probably running backwards, as they are brain dead in the real world.

Maybe I wired that car after a bender.

I have done this, so dont feel bad.

 

Yep, did that on my TR7, being a 20 y/o I called the RACQ and the dude reached under the right rear wheel arch and swapped the wires. His next question was "has the fuel pump been replaced recently". My reply, "about an hour ago"

 

Thanks for the inputs, the pumps are new and the issue is the same with the filler lids open. The car has been sitting in a friend’s garage since 2005 but he drove it in there. I drained both tanks and although the gas was old, it was clean. The pumps that were on the car were the originals and I didn’t think I should use them after all that time so I purchased new ones. The pumps are wired correctly and if I run a hose from my gas can to the pumps they prime and work as they should. There is no dual tank selector valve so I am going to run one pump for each tank, T the lines, and use check valves so the pumps won’t push back into each other. I currently have the assembly taken apart so I cannot attach a pic. Maybe I should ditch the electric pusher pumps and go with a mechanical puller pump?

 

???


1. Even if old, the English pumps could well be quite healthy. or respond to flushing out.


2. Two pumps indicate the car came from Brownslane with carburators. As the lump is apparently a carb'd engine. That should work.


3. As there are two tanks and two pumps, why is there not a switch on the dash to switch tanks and read the level on the guage for each?


4. Or are the tanks paired elctricaly and plumbed together by a "TEE"?


5. Perhaps the "NEW" pumps are for EFI and produce far too much PSI's for carbs?


6. Replicate the original and the SBC should be satisfied.


7. How have you dealt with the tank vent issue?


7. Yeah, You could replumb with simple T and use the mechanical pump.


8. The T system works but has just a bit of a limitation. don't park sideways on a steep slope with lotsa fue! The fuel from the up hill side tank will go to the down tank. if nt space there, on to the ground. then a stray sparka nd bye bye Jag!!!


Carl

 

There is a switch and that works well and when switched, it will apply power to the pump for that side. For the tank vents, there is a hose that runs down the side of the tanks and vents at the bottom by the tank drain.The tanks are run separately and TEE’d before going into the filters. The Holley RED pumps are 97GHP with a Max 7psi and designed for carbs. I have this same pump running on my T-Bucket. And I used it on my Z28. If I use check valves, the fuel can only come out and not in so there can be no transfer from tank to tank. Can it be possible that the pickup tubes inside the tanks are bad?

 

Normally, we use one inline electric pump and a 3 way Pollak or other changeover valve for carb SBC installs.

If EFI, hi pressure in line pump and 6 way Pollak changeover valve that uses the return lines.

My current XJ has a carb (waiting for them to ship the EFI system)... it has the mechanical engine fuel pump (will be removed and blocked off) and the three way changeover valve. It has worked perfectly since 1992.. I did not want to have to hear a electric pump all the time.. best place for a electric pump
is in the gas tank but that is a problem with the Jaguar tanks.. no one sells a conversion" for this purpose.

Pumps have to be mounted where the gravity flow will get into the pump(s) as they do not "pull" well but push fuel.

Pickups tubes in the tanks can be checked by running in a large tool.. doubt that is the problem... more likely the fuel pickup due to the pump
mounting spot not allowing gravity feed into the pump(s).


Lowest position on the trunk floor is the best place...

 

I'll look around for a change over valve?I had the pumps mounted on the floor below the tank fuel line so it should have worked. I plan on keeping the carbs because I have a small supercharger to be installed at a later date. I’ll try a single pump with the TEE and then I’ll probably go with the mechanical puller. I’ll also check the vent tubes and make sure they are open.

 

Simplifying to one pump is probably a good move overall just for simplicity and will help your problem solving. Normally the pump is below boot floor level in the space between the spare tyre and the rear bumper.

 

I'll try moving the pump to this location and see what happens. Hopefully I won't have to take these tanks out. I'm taking it over to have the exhaust work done on Saturday. I really want to hear this thing run, this cam should make it sound goooood. 2 1/4 inch back with glasspacks. We don't have emission requirements here so no cats are required.