4.2 Simple Dual Carb conversion

Hey folks.

I am looking for thoughts and recommendations for this kit car project I’m doing, and at some point this winter, I need to finalize engine details. I’m using a 4.2 XK6 from a 1977 Series 2 XJ6 sedan that has been rebuilt to stock specifications. The original intake was the awful water choke system and it’s long gone. My goal is simplicity and ease of maintenance. It’s only a 1,700 pound car, and I just want a reliable cruiser (not a track car), so I’m not looking for much. So in my head, I’m feeling like a dual intake manifold with twin carbs is the best way to go for many reasons.

If I were to find an intake manifold from a Series 1 XJ6, Jag 420, or some other 4.2 intake that used electric or manual choke and put on a set of dual SU HD6s or HD8s, is it as easy as finding the right jet needle to get it all to run correctly? (Or would a 3.8 intake also work?)

Bear in mind that I’m only talking about proper engine combustion. I know I’ll have to fabricate a throttle linkage, run the fuel line, set up a manual or electric choke as required. Just assume that these problems are solved for the sake of this discussion.

Thanks all.

The ASC is a pretty and very simple device. It works, and that’s all there’s to it. You know when it‘s on, and off, there’s no in between. And you can add a switch if you like.

Sorry the cap is so crooked, but I just pulled it out of a banana crate and cleaned it…

You can compare needles online - mintylamb.co.uk
I‘d try to get an idea from comparing the usual 4.2 needle (UM) to the needle used in the 2.8 Litre which also had HD8 carbs. You‘d be somewhere in the middle as a starting point.


I have twin Stromberg’s in my 2700 pound hot rod, with the same engine, and it works just fine. You really don’t need anything more than that.

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Wiggles, do you have suggestions on where to find dual Strombergs in decent condition? I’ve been given the impression that the XK6 Series 2 and newer Strombergs should be avoided.

Does it really matter if you utilize Stromberg’s or SUs: either set up will work fine for your intended purpose.

Nothing wrong with the Stromberg carburetors if they’re in good shape and they’re well maintained.

I would post a want ad on JagLovr’s looking for a set of either: somebody here has what you need.

I have a set of dual strombergs I took off my 69 type about 30 years ago have the manifold too
They worked great when I took them off so I would guess with a rebuild they would be fine. They have been in a heated building the whole time so …


Roger, I sent you a PM… hopefully. If you didn’t get it, lemme know.

I got your email. Postmaster said your email was down for maintenance . Will take some pictures and send a price over Friday … to your email thanks

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In my opinion (if you are determined to get rid of the Strombergs) the best is HS8

Standard on many S1 & S2 XJ6

They have a moveable Jet, so quite easy to convert to manual choke

The best choke conversion does away with the AED altogether (I have this)

You can get a choke conversion that converts the AED to manual control.
I do not know exactly how it works

The conversion kit on mine, it was not available last time I looked

It works the same as E-type HD8, in that it controls both Jet height and throttle position (E-type HD8 or conversions are too expensive)

It is possible to fabricate something similar

I believe @residentalien did something similar, apologies if I am wrong on that call :smile:

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I installed a dual set of 2" SUs with automatic choke on a 4.2 installed in my Mk1…Guess I got lucky, picked up the manifold and carbs on Ebay, slapped them on the engine and worked great, Did not even check the jets/needles that are installed.

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I prefer the manual choke setup as the E-type had. My 420 was converted tothat style and so will my mk2. The hisser can spit fuel back and ignite and the garage smells of gas regularly as the top is pretty much open.

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If you have manual choke carbs, the North American E-type Stromberg emissions control manifold can be easily stripped back to its fundamental base and modified to accept 2 H8 or HD8 carburetors. Since so many cars get converted to the earlier 3-carb setup, the Stromberg manifolds are dirt cheap.


Hi, I suspect you are in US which would complicate things, otherwise I have a complete manifold with reconditioned HD8 carbs from a very early Xj6 for sale. I am in Sweden.
Br Svante

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