1977 xj6 two fuel or one?

[RobXjcoupe]

So I’m looking at the original fuel tanks on my 77 xjc and they need replacing in simple terms. Both in tank fuel pumps I’ve tested and both don’t work.
My question is for simplicity sake and possible future maintenance, if I replaced both tanks and then connected the fuel tanks as per the fuel injection version using a single fuel pump mounted in the boot with the change over valve to keep a bit of Jaguar originality what fuel pump should I use? Would a series 3 injection fuel pump be ok for the carburettors or too much pressure?
Any information would be gratefully received

[Piersman2]

Have you taken put the fuel pumps and chceked them over. I remember extracting and cleaning the two fuel pumps on my old XJC as they couldn't deliver enough fuel to the carbs. Turned out the filters inside the tanks were clogged with ste.

Cleaned and flushed the filters, drained the old fuel to get rid of particulates in the bottom the tank, and all good after that.

IIRC there are tank drain plugs at the bottom of each tank?

[RobXjcoupe]

Piersman2 said:

Have you taken put the fuel pumps and chceked them over. I remember extracting and cleaning the two fuel pumps on my old XJC as they couldn't deliver enough fuel to the carbs. Turned out the filters inside the tanks were clogged with ste.

Cleaned and flushed the filters, drained the old fuel to get rid of particulates in the bottom the tank, and all good after that.

IIRC there are tank drain plugs at the bottom of each tank?

I’ve totally removed both tanks. One tank had been lined with some kind of bitumen with the pump in situ and to remove that pump was grief as the filter had become part of the bitumen lining. Once removed I checked the pump on the bench and absolutely nothing. Second tank the pump was removed a lot easier. Checked that pump and that too was kerput with nothing moving when power applied.
The tank with bitumen has obviously been repaired before, as the bottom edge had braised repairs carried out. With the rear axle and heat shield off it was found the link pipe between both tanks was badly corroded and that also needs replacing.
So just as an idea I thought of using one external fuel pump like the series 3 xj6 and do away with two internal fuel pumps. I assume the series 3 pump creates to much fuel pressure to supply carburettors so use an inline fuel pressure regulator to bring it down to 4psi. Looking at new tanks they don’t come with the pipework fittings and I can’t seem to find any new ones or the details in measurements to make them
Fitting new in tank pumps and tanks is ok but from a maintenance point seems to be a backward move while the car is under going all this work

[ruhall]

The series 1 and earlier series 2 [pre-77](6-cylinders) had two single-action SU contact-breaker fuel pumps in the bootwell. Is that an option?

[RobXjcoupe]

ruhall]The series 1 and earlier series 2 [pre-77 said:

(6-cylinders) had two single-action SU contact-breaker fuel pumps in the bootwell. Is that an option?

Looked at that set up. The series 3 just uses a single pump in the bootwell. So will use that installation as it’s one less pump to maintain. Now I’m really after are the outlet pipes that bolt onto a new fuel injection tank. Any ideas where to get those from?

[ruhall]

The 3.4 Series 111 were carb IIRC; it would be interesting to know what pump they used, whether it was different from the 4.2 injection.

Have you tried Rimmers or David Manners (other specialists are available )?

[RobXjcoupe]

ruhall said:

The 3.4 Series 111 were carb IIRC; it would be interesting to know what pump they used, whether it was different from the 4.2 injection.

Have you tried Rimmers or David Manners (other specialists are available )?

So many variations of the same thing lol been having a think. I could use the now broken fuel pump outlet pipe, remove the old pump and wiring and just lengthen the pipe into the tank accordingly with a filter on the end as if a pump were fitted. Then use that as an outlet for a series 3 pump to suck out the fuel via a bootwell mounted fuel pump. If a series 3 3.4 carb engine uses a low pressure pump then no need for a pressure regulator. So I’ll research that and see if that’s any different

[Jaguar steve]

RobXjcoupe said:

ruhall said:

The 3.4 Series 111 were carb IIRC; it would be interesting to know what pump they used, whether it was different from the 4.2 injection.

Have you tried Rimmers or David Manners (other specialists are available )?

So many variations of the same thing lol been having a think. I could use the now broken fuel pump outlet pipe, remove the old pump and wiring and just lengthen the pipe into the tank accordingly with a filter on the end as if a pump were fitted. Then use that as an outlet for a series 3 pump to suck out the fuel via a bootwell mounted fuel pump. If a series 3 3.4 carb engine uses a low pressure pump then no need for a pressure regulator. So I’ll research that and see if that’s any different

Yes the 3.4 Series 3 was on carbs and not injected like the 4.2

My (very late) Series 3 3.4 had a tank side mounted combined pump and filter and level sender submerged in each tank with a changeover vale on the rear valence inside the boot. No pressure regulator needed. IIRC there was a one way valve between each tank to stop the pump from one filling the other one up when it was running rather than supplying the engine.

There was a drain plug at the bottom of each tank too.

[melhookv12]

I wouldn't use an EFI pump on a carb engine.
They produce to much pressure.
You can buy a Facet pump for not much money, you would still need a regulator.

[RobXjcoupe]

melhookv12 said:

I wouldn't use an EFI pump on a carb engine.
They produce to much pressure.
You can buy a Facet pump for not much money, you would still need a regulator.

I was thinking of trying to keep the parts Jaguar, obviously a regulator wouldn’t but can a fuel pressure regulator reduce an efi fuel pump sufficiently?

[Jaguar steve]

RobXjcoupe said:

melhookv12 said:

I wouldn't use an EFI pump on a carb engine.
They produce to much pressure.
You can buy a Facet pump for not much money, you would still need a regulator.

I was thinking of trying to keep the parts Jaguar, obviously a regulator wouldn’t but can a fuel pressure regulator reduce an efi fuel pump sufficiently?

Something like this? Contemporary '70s fuel pressure regulator.



Back in the day IIRC max input pressure for these was around 10 psi which is about the best you'd get from a mechanical engine driven diaphragm fuel pump. Early Bosch Fuel Injection was regulated at region of 30psi so a efi pump was/is capable of delivering way more than that regulator can handle.

[RobXjcoupe]

Jaguar steve said:

RobXjcoupe said:

melhookv12 said:

I wouldn't use an EFI pump on a carb engine.
They produce to much pressure.
You can buy a Facet pump for not much money, you would still need a regulator.

I was thinking of trying to keep the parts Jaguar, obviously a regulator wouldn’t but can a fuel pressure regulator reduce an efi fuel pump sufficiently?

Something like this? Contemporary '70s fuel pressure regulator.



Back in the day IIRC max input pressure for these was around 10 psi which is about the best you'd get from a mechanical engine driven diaphragm fuel pump. Early Bosch Fuel Injection was regulated at region of 30psi so a efi pump was/is capable of delivering way more than that regulator can handle.

No worries, way too much pressure from an efi pump then. Carburettors would be spewing fuel left right and centre. A 4psi facet pump it is then

[melhookv12]

I would mount the pressure regulator under the bonnet as close to the carbs as possible.
You might lose a small about of pressure on the run up the length of th he car, which might cause you fuelling issues that you can't find.

Basically, you think you have good pressure in the boot ( 4 psi ), but when it gets to the carbs it's down to 3.5 psi. If you get what I mean.

Or fit a fuel pressure gauge under the bonnet.

[RobXjcoupe]

melhookv12 said:

I would mount the pressure regulator under the bonnet as close to the carbs as possible.
You might lose a small about of pressure on the run up the length of th he car, which might cause you fuelling issues that you can't find.

Basically, you think you have good pressure in the boot ( 4 psi ), but when it gets to the carbs it's down to 3.5 psi. If you get what I mean.

Or fit a fuel pressure gauge under the bonnet.

That makes sense. Thank you

[Peter3442]

So long as you are sticking with carburetors, I would find the space in the boot to use two low pressure pumps.

The standard Jaguar change over valves for the fuel injected engines are a pain, a severe pain. They are not very reliable, especially the one in the boot that selects which tank to take fuel from. They are sensitive to dirt in the fuel and are likely to get gummed if you don't switch them fairly regularly.

I realise that with the system you are proposing you'd need only the one, but it is in my experience the worst one.

If you go ahead with the swap, use a non-Jaguar change over valve.

[RobXjcoupe]

Peter3442 said:

So long as you are sticking with carburetors, I would find the space in the boot to use two low pressure pumps.

The standard Jaguar change over valves for the fuel injected engines are a pain, a severe pain. They are not very reliable, especially the one in the boot that selects which tank to take fuel from. They are sensitive to dirt in the fuel and are likely to get gummed if you don't switch them fairly regularly.

I realise that with the system you are proposing you'd need only the one, but it is in my experience the worst one.

If you go ahead with the swap, use a non-Jaguar change over valve.

So you’re saying basically fit two boot mounted pumps as the original Jaguar fuel injection Change over valves are a bit unreliable. My car has original wiring for 2 pumps anyway so just make it a boot mounted feed like the original series 1 xj’s. Then it’s a simple switch between pumps with the non return valves plumbed in accordingly.

[Peter3442]

Rob, that's what I would do. If you search series 3 XJ change over valves or fuel tank overflowing on a few Jaguar forums, you'll see that it's a recurrent problem, probably the most unreliable part on a series 3 XJ. I've been tidying my garage the last couple of weeks and found four that I've taken off, cleaned and kept as a reserve for 'next time'. When the next 'next time' comes along, I'll buy a completely different type that is made for motor yachts.

[RobXjcoupe]

Thank you Peter, duly noted

[melhookv12]

But being carburettors, does it still have a return to the tank ?
I know the efi does as this is where the excess pressure goes.
My v12 ( 6x Webbers, facet, pressure reg as above ) didnt have a return to the pump.

I've never looked in the boot of a s3 with carbs ( well I have but I can't remember the layout )

[RobXjcoupe]

No return on my carburettors car. Overflow straight on to the floor via the top of the float chamber if the internal valve fails. Probably the reason just a 4psi pump as the carb float overflow valves are tiny and wouldn’t resist much pressure