Modified 73 XJ6 Triple SU Manual Swap Build Thread

I picked up a 73 XJ6 project the other daaaay…( a couple years ago), and it’s been in storage untouched ever since. I initially bought it because it’s rust-free (basically) XJ6 Series 1, short wheelbase, 98% complete, and it’s especially interesting because someone has swapped in a manual transmission and triple SUs from what I believe is an E type or Mk10. This is a California car that still has blue plates with stickers from 1989. I have a full time job as an industrial designer, but I do run a small non sponsored youtube channel where I document all my builds; here’s the first video on this build, please consider subscribing if you don’t want to miss future episodes:

Alright, so I just dragged the kitty back to my house to get this thing roadworthy, yesterday:

First step: Get it running

Now, I have heard this car start and grumble on starting fluid when I bought it 3 years ago, but there seems to be a fuel issue now… mainly the fact that when you turn the key, I hear the fuel pump turn on, and fuel starts pissing out of the bottom of the engine compartment. I’ve narrowed down the leak to a fuel line that runs right about here:

It’s a small black hose that is absolutely pissing fuel at a huge rate, creating a giant puddle. I’m a complete newb to these cars, but I’m expecting I’ll have to pull the carbs to access this area. While doing this, I’d also like to drain the fuel tanks, and replace the fuel filter. I believe I’ve found the fuel filter in the trunk, near the spare tire, barely visible in this photo:

How would I go about draining the tanks? Is there a drain plug somewhere on the tank itself? Is that was those things are behind the rear wheels?

Thanks for the help, and if you don’t want to miss the next episode, make sure you subscribe, but again, I have a real job so I’m not going to beg you guys. You either find it interesting or not, do whatever you want.


Yes, the two short bolts (9/16 in) below the fenders. They screw into a larger threaded insert; make sure you’re not turning that or you will need to replace a gasket. Your photo doesn’t show the leak, at least that I can see. There are three hard overflow lines that will leak if their corresponding float valves get stuck open, or the float is sinking.

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Sorry I couldn’t be more clear in the photo, the … component, idk what it is, between the rear and middle carb, that has two hoses going to it. That thing appears to have a small hose going straight down, then towards the block. That is SPRAYING fuel. Very strong flow.

We can’t really see what setup you have there, but it looks like a 3.8 manifold, not the later 4.2 one. Do you have a manual choke setup? If not, the 3.8 Mk 10 used what is called an Auxilliary starting carburettor ( ASC) which is electrically controlled and is usually mounted between carbs 1 and 2, I think. This takes fuel from the front carb fuel bowl and feeds it via a solenoid operated metering device into the inlet manifold via tiny metal pipes. That could be flooding, or simply stuck floats as mentioned previously. If you can show us a better photo with the bracing rod and air cleaner removed, we can possibly be of more assistance.

I can’t get a better photo unless I remove parts, but in person, I can see it pouring out the side of a small black line. It’s a stream coming right out the side of a split hose. If anyone knows what that might be so I can order a new hose, lmk, otherwise it will have to wait until I get in my garage to start disassembly.

Sure sounds like an overflow, as I suggested before. Use the excellent archives on this site. “SU overflow pipe,” “stuck SU float valve,” etc. If the front float valve is stuck open it will also overflow from the starting carb as Kevin mentions…if you have the Mark X setup. Overall you need to familiarize yourself with what you have IMO.

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Depending on what has been modified, there is a fuel bowl\filter setup mounted on the right inner guard beneath the air filter.
The outlet from that goes via a flexible line to the hard lines connected to the carbs.

Does your setup have one of these? This is the ASC

and the big tube goes under the manifold and separates into 6 separate lines that go into each inlet port throat. I suspect your problem is a split flexible line and you can probably repair it with normal fuel hose.

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[quote=“ADDvanced, post:1, topic:427099, full:true”]
It’s a small black hose that is absolutely pissing fuel at a huge rate, creating a giant puddle. I’m a complete newb to these cars, but I’m expecting I’ll have to pull the carbs to access this area.

Quite likely - it’s either a sunk float or failed inlet needle valve. Which requires removing the float bowl, which may be difficult without removing the carbs…

In theory; excessive fuel pressure may overwhelm a needle valve, but not to the extent of ‘full overflow’. You could check fuel pressure - 4 - 6 psi is adequate. Do you have external or submerged fuel pumps?

There is no reason to drain the tanks to change external filters, clamping the hoses is adequate. And failed in-tank, or other, filters will not cause overflow…

xj6 85 Sov Europe (UK/NZ)

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I see no ASC (Auxilliary Starting Carb) in the OPs photos, which would have been standard on a MKX or 420G, and I cant even tell what manifold it is off

I do see what is the same shape as an AED (Automatic Enrichment Device) directly under the OP finger in one of the pics

The OP should examine the vehicle closely to see if there is any evidence of a Choke cable or assembly, which would be indicative of E-type HD8s. It may also have HS8s

If that AED is placed where it is, or no ASC, that is a PO modification that will be troublesome until diagnosed

Your fuel leak is almost certainly caused by a jammed needle & seat, failed float, or faulty auxiliary carb, or associated fuel lines

These will all cause fuel to flow out at full pump pressure

at least you know the fuel pump is working

I would remove all air filter assembly, and remove the fuel bowl lid on the leaking carb, as an absolute minimum. A gasket is needed for the fuel bowl lid

You need to sort out by what means this one has been modified to start, as it will not start and run well, if at all, until that is sorted

Given the time in storage, and since it has run, I would expect the carbs would probably need to be taken apart, cleaned and have perishable parts replaced

This can be done by the average home mechanic, there is enough info in the archives here, and Youtube etc etc

warning, fire extinguishing gear should be nearby when this fault exists

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Maybe a home made manifold. I thought the Mk 10 manifold positioned the front carb too high for the bonnet to close without modification, which was why the E Type one , which drops the carbs down is preferred. But the 3.8 one uses 3 seperate castings, while the 4.2 one has the water rail cast in; this doesn’t really look much like either of them. Better photos would help. I agree, sticking float is the likely culprit be he says it is leaking from a small hose coming from something between the rear 2 carbs. The ASC is normally attached to the front carb, I think, but that carb could easily be located as the middle one, or the ASC connected to it anyway. Either way, dismantling is required, air cleaner off would be a good place to start.

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Buy the s1 workshop manual. It’s red, cheap and really useful.


Sorry I couldn’t be more clear in the photo, the … component, idk what it is, between the rear and middle carb, that has two hoses going to it. That thing appears to have a small hose going straight down, then towards the block. That is SPRAYING fuel. Very strong flow.

(My quote function isnt working for some reason, but)

What you are pointing at definitely appears to be an AED,
I have some here, but am not familiar with the fuel hose arrangement

These are known to be a fault prone device, but can be repaired. (I have seen them fitted with a mower fuel on/off tap)

Standard for S2 XJ, need better pics, your hand is partly obscuring the item

I assume you have checked its not just a spilt hose, or bad clamp

this guys Youtube will allow you to ID if you have one or not, and he gives good instruction

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It appears your SU’s are from a 4.2 E-type. You have short bell SU’s (an e-Type thing) and more importantly no visible starting carb so not Mk10/420G. My 4 speed MOD car has a Mk10 manifold. Starting carb is visible between front and center carbs. I had my bells shortened to E-Type height to fit under the hood.

Yours appears to be a US spec car which would have originally had 2 z-s 175 cd carbs and a choke cable. You have what appears to be the original air cleaner for the car modified to fit 3 carbs instead of 2. That thing you’re pointing at looks like the housing for a thermostatic Vacuum valve that controls the butterfly for the air cleaner hot air intake - shouldn’t have any fuel there under normal circumstances.

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I appreciate all the replies, so I’ll do my best to respond to them. I am a fast learner, and I’ve been reading about this thing non stop for a few days both on these forums and other nuggets I’ve found on the internet. Also this happened:

The Bavaria was an impulse buy last week, idk… I used to have a 1971 Bmw 2002 the same color and I just had to have it. Weird seeing these things side by side, given that they were produced within a year of each other. So similar (I6, rwd, 4 disc etc) but soooooooo different. Bavaria feels absolutely like a Camry compared to the jag in so many ways, but at the same time the BMW is much more modern in most of it’s design. It’s been off the road for 41 years at this point, and you can watch an overview of this car and my attempt at getting the engine running in this video:

I say attempt because, well, that engine is junk, I don’t know what I’m going to do with it yet. Either way, need to focus so…

This was my lunch hour today, playing musical non-running european cars in my driveway; I dragged the 72 Bavaria into storage which means I didn’t have time to get back to the jag until after dark. Another shot of the Jag just cuz:

  • I did read about the stuck float/overflow pipes, which it could still be, but what’s weird is it looks like a black cable that runs towards the block. It’s extremely dirty, I haven’t pressure washed this engine bay yet, and it might be a bent overflow tube, kinked, and spraying out the side. Need to start taking things apart to clarify.

  • I want to drain the tanks because the fuel is at this point, 5 years old. When I have free time I’ll crack the drains and use it for a campfire or something. Once I get the car running, I plan on changing the all the fluids entirely.

  • I’m not sure what intake/carb setup this is either. I plan on removing it all, going through the carbs, and replacing the intake/carb gaskets, as they looked absolutely roached. This means I need to start ordering parts. Can someone help identify what I actually have here, so I can order the right carb kits/intake gaskets?

I’d like to place an order for carb kits, intake gaskets, valve cover gaskets, and… idk really looking for suggestions here. My plan here is to go through the fuel system, and once that it nailed down I’m pretty sure she’ll purr, since I heard this thing run on starting fluid a few years ago.

@davidsxj6 you mean this?

I have been reading it nightly, and learning a ton, but there’s not a good view of the overall fuel routing under the hood, just technical info about rebuilding the carbs, the fuel pumps, etc. Is there a better source to understand the fuel system from more of a layout/component by component level? Or a diagram that shows the entire fuel system?

@RustfreeMike It appears we have a similar setup then, as my intake matches yours. So it’s a Mk10 manifold… with ‘short bell’ SUs? How do I further ID these carbs? I want to order parts for this asap so I can start tearing into this next week.

Also, from reading the service manual, this definitely still has the air pump and all that smog garbage since this is a california car. Is there a good how to on removing all this crap, and is it worth anything or should I toss it into the dumpster? This car is modified, not original, so I don’t care about the smog equipment one single bit.


I agree with Mike the rectangular object is a thermo vacuum valve not an AED

It appears you have HD8 carbs, but I cant see evidence of choke mechanism (that raises & lowers the jet from below)…ie E-type parts, (which are valuable)

I cant see an ASC either

I think that may be a 420G manifold, but am not fully familiar with the E-type manifold

You need to remove the air cleaner apparatus to take better pictures, and give you better access to work on things

you have a customised setup, I have done a few, and it can be hard to tell what has been done without it being pointed out

I advise exercising some patience, in working out what you have, and any faults
All HD8 carbs have the same overhaul kits (as far as I know)

They may not need a full overhaul

I’ve been looking around, and it sure looks like this set on ebay is what’s on my car:

If that is the case, I’m just going to try to start tracking down valve cover gaskets, intake gaskets, and carb rebuilts for an E type, and I think that should work. Thanks for your help! Any other gaskets that are super common leak points I should address? Would like to just have all the gaskets I need to cover the main problem areas.

I do have a choke cable inside the car, but I’m not sure if ti’s hooked to anything. I’ll go check right now.

Edit: Just checked. There is a choke lever in the car, left hand side of the steering wheel, that clicks fore/aft. I had my girlfriend mess with it while I looked at the carbs, and saw no sign of movement in any of the linkages.

They’re SU HD8’s from a 4.2 E-Type. This part of your pic shows part of the manual choke assembly:

That system drops the jets for starting enrichment when the cable is pulled via a pushrod system under the carbs. The manifold passages are the same for the various 4.2 triple SU applications. Thermostat area has some variation - need to see that better.

Mk10/420g has a metal isolator with orings and springs between the carbs and manifold which you don’t have. You have the E-type carb spacer between 2 gaskets sandwich and short bells. I think it’s pretty safe to say your system is from a 4.2 E-type.


Definitely disconnect the air pump belt because if it’s still blowing into the ports in the head you will occasionally get a serious backfire on overrun if you drive hard because this manifold doesn’t have the gulp valve that mitigates that issue.

This car would’ve also had fixed orifice EGR but because of the carbs the only remnant of it would be a port on the top of the rear exhaust manifold - shove a bolt in it if it ain’t already blocked.

Being a smog spec 73 it would also have a vacuum retard distributor. This is designed to only operate at idle and those carbs don’t have that functionality. If it is connected and it is a functional vac retard capsule disconnect that too. I see you have a line coming out of the top of the front carb - this would supply ported vacuum to the earlier vac advance dizzy. Hopefully it isn’t connected to the original vac retard dizzy. If so, like I said, disconnect it and block the line until you can get a proper distributor.

One other thing is the anti-run-on valve but there’s nothing it can really do to those carbs so even if it works all you need to do is disconnect it. It’s a small metal cylinder under the brake master cylinder area.

That’s about it for pollution parts - at least the stuff that’s left.

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You got lucky with these carbs.

Fuel comes from the pumps and filter, enters through the right* wheel well, goes to the cooler (with the AC lines) and then to the three float bowls in your case. If a float is stuck or leaks it will go out the line at the top of the bowl and towards the ground.


Alright, ordered a lot of parts, but today I plan on popping the hood and pressure washing a few decades worth of grime from this thing. Any parts of the engine bay I should really avoid with water pressure?