Xj6 1973 s1 dumping fuel onto the ground & wont start or run

Hey everyone. Im new to the jaguar scene. Im still diving into cars and trying to find out how deep the rabbit hole goes with engines. So my dad threw this 1973 s1 xj6 at me and said “here, restore it!!” Short story long. Ive replaced the battery, both fuel tanks,fuel sending units, fuel filter and air filter. Shorty after i put 1 gallon of 93 into both tanks, tried to start it and it started dumping fuel onto the ground from the pipe that is supposed to be hooked up to the charcoal canister. Also still wont start.

Can anyone help with diagrams on how the fuel connects to the emission hoses?

It goes deeper than that, Steven…

Assuming you have carbs and two submerged pumps, or one or two pumps in boot? I ask to clarify; POs sometimes change from original set-ups…:slight_smile:

Fuel leaking from the charcoal canister implies that the selected tank is ‘overflowing’ - usually due to one tank feeding into the other due to a ‘changeover’ system fault. Your extra fuel may have added to the problem.

First; select the other tank - the overflow should stop. The engine may still not start due to other problems, but the overflow should stop - it’s a diagnostic procedure…:slight_smile:

Report back - and welcome on board!

xj6 85 Sov Europe (UK/NZ)

Frank, the carb engines don’t have the overflow issue as the fuel is only pumped forward and once running pressure is achieved the pumps stop and await further need. This makes it very much simpler than the S3 EFI setup.

Get a workshop manual, otherwise you’re lost. That has diagrams of the fuel system and much more. Just a gallon in each tank?

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I have a carbureted engine with the 2 carburetors. The reason why i only put 1 gallon in each tank is because 93 octane is expensive here in the US, i know as soon as i turn the key its going to start dumping gas out of the line and im not about to fill them up just to watch all that gas go to waste. Also i have 2 external SU pumps.

This is the evap plumbing.

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Thanks, my charcoal canister is in the driver wheel well. I read on another thread it could be my floats are clogged and the fuel that cant make it to past the carburetors could be forced into the evap system. Does this sound right?

Thanks everyone.

With two pumps, Nick, their output must joined at some point to deliver to one fuel line. This means that one pump running will deliver both to the fuel line and the other pump.

The usual way to avoid crossflow to the tank through the ‘idle’ fuel pump is a one way valve on each pump. If this fails there is usually adequate pressure to fill the ‘wrong’ tank.

There are various ways of solving this ‘crossfeed’, two into one, problem of course and, as you say very reliable on carbed cars - hence seldom encountered.

My rationale is that fuel entering the carbon canister must be due to overflowing tank - and that fuel can only come from the other tank. With a single pump the problem cannot arise; it has only one pressurised output - and two feeds to be sorted. Usually a changeover valve…
On EFI the, arguably ‘frequent’, failures are that three ‘vulnerable’ components are involved…

xj6 85 Sov Europe (UK/NZ)

Not really, Steve - the tank venting system and the pump/carb lines are ‘entirely’ separate. And with a stuck float the carb itself would overflow…does it?

Again; just switch to the other tank to see what happens…to clarify one issue…

xj6 85 Sov Europe (UK/NZ)

I do see a little fuel on the passenger side under the “bonnet” and under the carburetors on the frame. Also since i had the car ive only put 2 gallons into each tank so i cant see them overflowing because even if you put both tanks together 4 gallons isnt enough to make either side overflow right? Ive switched back and forth, same result when i try to start the car.

Does anyone have a picture of these change over valves or the location there in because i cant find mine? Are they bolted behind like the rear suspension or is houdini hiding them from me🤔

There are no changeover valves in the carb system. The pumps only flow one way and the changeover switch just powers up one pump of the other.

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The poppert valves of the pumps do this, although my tanks do equalize over weeks…
S1 only have pumps and a T junction.

I guess I need to look and see if someone connected something wrong. If there’s no way for the fuel lines to somehow connect to the evap system.

I’d help, but mine doesn’t have emissions stuff… I don’t see how it can be connected correctly though.

Thanks for trying!

What do the petrol gauge read on either tank, Steven. You added two gallons, which certainly is not enough to overfill the tanks - but how much was there before…?

Trace the hose from the canister to the engine - and see where it connects. It’s there to draw petrol vapour from the canister by engine vacuum when the engine is running.

This the only other way fuel can be delivered to the canister - so the connection location must be verified. I cannot see how this can happen, even if the carbs overflow - which in itself will cause a non-start…

You can disconnect/clamp the canister to engine hose to see what happens - the hose plays no part in engine running. But as the engine is likely flooded and something is likely wrong with the carbs - the starting problem may remain…

xj6 85 Sov Europe (UK/NZ)

So when i got the car i emediately replaced both tanks and sending units. Both tanks were empty because they were leaking before i replaced them. Since i replaced them ive only added 1 gallon to each tank. When i try to start the car fuel flows out of the of the bigger hose that should be connected to the canister. Ill trace the big hose back to where it connects to.

Sorry about my conclusion jumping, Steven…

There should be no ‘big hoses’ related to the tank ventilation system - basically vacuum hose dimensioned. Connected at each tank’s filler necks, above max fuel level, each go up to fuel separators in the C-pillars. One hose there then goes back to the tank lower level to return liquid fuel to the tank.

Remaining hose from each separator may join up (‘T’) above the rear cage with one single hose goes forward, or there may be two separate hoses to the canister. One hose at the canister goes to engine - and the canister is vented to open air by a ‘big’ hose. It will leak fuel if fuel for some reason entersa the canister - but is not the cause of it…

With the engine not running, eventual fuel vapour is adsorbed by the charcoal in the canister before venting to open air. With the engine running, the adsorbed petrol is drawn out of the charcoal by outside air through it, into the engine - to be burnt…


xj6 6 85 Sov Europe (UK/NZ)

It sounds like you have connected the pump outlet to the Evap system, not the pipe to the carburettors, or the return from the carburettors to the evap system pipework.

Just follow the pipes along the car from front to back and connect accordingly.

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