my main aim is to NOT use the longer studs.
They make removing a carb agony. The shorter studs, its much easier
the springs are a pita as well, easy to lose one or more
most likely follow your advise and use the flat phenolic plates and gaskets (as per XJ HS8)
I think, (but could be wrong) that the o-ring style metal plates could also be used in place of the phenolic, with short studs, spring washers and nuts, no springs
Hi @Robert_Wilkinson and @awg Mine is 420G only when it comes to the idler shaft that operates the 3 HD8’s I still use the original S1 XJ linkage (with a different welded arm) and a hybrid shaft that connects to the 420G idler and the S1 linkage.
@Awg Tony your setup is looking great… but are you connecting the 3 carbs together with those pinch springs and intermediate shafts? @Robert_Wilkinson Bob didn’t you have trouble with that method?
I too hate the hisser - but I connected mine to the original S1 XJ choke indicator light circuit so I can control it with the original choke lever from inside the car instead of letting it do it’s own thing.
~Mike
Hi Robert
the no WOT issue is probably because max cable travel < max throttle shaft movement needed?
I spent along time calculating the exact distance of all needed pieces, and levers X 2, as the trans pressure cable travel also needs to be perfect, on a BW8 its critical, and I needed to make new brackets to ensure everything was to ± 1mm, with adjustment capabilty
If you are able to post a pic of your throttle cable/bracket setup in here, that would be helpful
The present setup in the car is twin HS8 with Burlen full manual chokes, (shown in my 2nd post) everything is working there, so I will transplant those 2 carbs, and all parts onto my 420G manifold at fitment time, using shorter shafts
At that time I will take closeup pics of all the pieces
before I forget, lister @residentalien did a twin HS8 setup with homemade manual choke
I will also link in an E-type guy from another forum did a cable throttle conversion
next up, finish of the throttle rods & connectors, clean up the 420G manifold to a high standard
Correct, Tony. I did no calculations, in fact I wasn’t even thinking about the ratio at all. So I get not quite to WOT.
Another variable, that I believe I read about rather than discovering it myself, is the “transfer function” between pedal depression and actual throttle opening. Besides the nonlinearity of the butterfly’s effect on throttle opening (big difference when nearly vertical, little difference when nearly wide open) there is a nonlinearity associated with the angle of levers connected by a link (most linear when parallel to each other and perpendicular to the link). It’s more complicated still by difference in lever length (to get correct range as you calculated). You might wind up with a lot of throttle movement at the beginning, or a lot near WOT. There’s an optimum for all of this in terms of how you perceive acceleration or cruising speed versus pedal depression. Beyond my pay grade, but I did notice that my levers are a kludge in this respect.
Hi Robert
I had to do trigonometry to make sure it was right, so that the arc of travel of my throttle and kickdown cable matched the cable travel.
I added adjustable ends. so that the cable can be very responsive to throttle.
Better imo than the original setup
here is a link to an E-type guy that did similar…it takes a bit to get to his pics, but b4 I forget
I had to spend a bit of time getting the return springs.
Basically, added a short strong spring that only activates near WOT
I relied upon Jaguar Engineers to take care of this issue, adopting a system based upon XJ6.
The cable travel at the pedal lever = cable travel from closed to WOT, in my case ~38mm, and its linear with a cable system.
My setup also uses the XJ carb linkages
spent a little time experimenting and researching.
The Burlen SU website sure is weird!!, parts that do not show up on their site can only be found via Google…IF you have the correct SU part num
also found there are a few different ways to manually choke HS carbs
I will list the various methods and SU part nums required to do this soon
It can be done easily, for less than $100 for 2 carbs, for a basic setup
spent a few hours dismantling and cleaning parts,
still waiting on a few bits to arrive, and it will be fully assembled, and operational
have to fabricate some more brackets for the 2nd choke cable, basing it on the XJ12 twin cable setup
my total spend on parts so far is only about $60
this is the most basic setup…for setting up twin carbs, also applicable to triples
gent reckons you can just use these SU parts
WZX 871
https://sucarb.co.uk/hs-throttle-and-choke-interconnection-kit.html
AUC 1426 x 2
https://sucarb.co.uk/bolt-19493.html
total cost about 30GPB
only activates jets, not throttle
You can order the actuating end lever separately as part
AUE 586 or AUE 587
GBP 7 each…but u can use the same part, they are not really handed
In the “simple” version, these have to be bent (afaic) to engage the choke parts on the HS8.
I tested this on my setup
imo, an additional jet return spring should be added (externally, to the lever)
this setup lacks the circular jet return springs
Part Number: WZX 1335
Description: Choke return Spring Kit HS Carburettors Standard Jet Left Hand
Part Number: WZX 1336
Description: Choke return Spring Kit HS Carburettors Standard Jet Right Hand
I am off the opinion these could simply be added instead of an external return spring.
My setup has them, they are only a few $
Version 2
from UK Ebay…virtually the same thing, but as a whole, only much more expensive.
(250GBP, not including choke
The actuating levers are slightly different
they can be ordered separately as SU parts
AUE 236…or 235…a grade 8 bolt can be used to actuate the HS8 choke lever
…examine the pics on Ebay, you can see how it is done
like this
meid%3D09038b566e384ebbb41eb961a00b9f37%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D372649724535%26itm%3D323771246675&_trksid=p2047675.c100009.m1982
here is the choke cable I use
$35, the locking facility is preferred
here is what I currently have have fitted on the twin HS8 XJ motor in my 420G, the “king” of systems, complete with levers that are actuated by the choke, and act upon the throttle, so that dropping the jet also boosts throttle, adjustable via a stop screw, parts numbers vary with Carb, but believed to be AUC 2610/11 for an HS8
These parts are not listed. Another poster fabricated them
For some unknown reason, the pivot bolt shown in this Joe Curto pic is NOT the pivot bolt that receives a shaft…there is another part that can also be used that eliminates the connecting shaft.
here is a very good close up of a Mini HS setup, clearly showing the way the linkages work
It shows the pivot bolt AUC1426 that receives the connecting shaft, and also the circular springs that return the choke/jet lever
I have a pair of HS6 carbs, with a full manual choke setup, as above, the body is marked AU9, which SU call out as Volvo (via Google search)…all the parts can be used on an HS8, although they are slightly different
This is all distinct from the kit that acts directly upon the AED
All the above mean the AED is removed
I will add more to the thread via edit
almost fully dressed for battle, setup using a V12 XJ dual choke setup salvaged from a wreck.
parts from that mechanism will be used to run from the existing locking choke I have setup, as it wont easily fit the V12 brackets in my cabin. I really like the positive twist/lock action of the existing cable, a micro switch & led will be included, as per the V12
the front carb choke setup, 5mm bike cable parts, a small bracket made,
the only mod is a 1.5mm hole drilled to take a split pin that retains my choke bracket
unfortunately the project has to go on the back burner a bit, as I have to design & make about 5 brackets, test fit everything, allow time for rework etc etc, but have other work to finish off before annual rego inspection, so I will have to wait till after that to fit the unit to the car
It looks really nice,Tony.
it will look much better when everything is polished, only the front carb in that setup is being used, not the rear 2, or manifold
It actually looks very similar to the HD8 setup, minus the ASC
Only someone that was very familiar with SU carbs would be able to detect they are not HS8
the finished article will probably have SS braided air & fuel lines, like the dual HS8
fuel & vacuum lines fit, using original Jag parts
I am going through the engineering of my throttle linkage with a view to overcoming some issues
Issue 1; pedal goes through a point of binding, fixed…linkage under pedal has an adjustable plate, loosen nuts, and it “self-adjusts” No more binding
issue 2 ; pedal has lateral movement, and when taken apart, the special double shouldered bolt, and/or the pedal barrel itself is worn somewhat, so the bolt is slightly sloppy.
My spare bolt with pedal assembly is worse, this is a bad area on 420G, as its hinged to the floor, in a bad area of moisture, and no one pays much attention until its almost too late. I have previously rehabilitated this area. I partially reduced the lateral movement by tightening the nut a bit more. Hopefully this part is available new, otherwise a lathe would be needed to make a correctly sized replacement
issue 4…this part C34388 throttle shaft rubber bush is presumably flogged, as the throttle shaft has lateral movement, translating to much hated “slop”
Part ordered, should be here in a few days $15
issue 4, and the biggest one of all
AAs previously mentioned, its imperative the kickdown cable on a BW8 be perfectly in sync with throttle, as that is the only input that controls gearbox function (although it has an internal governor)
At present, it does do that, but the throttle does not open fully. With slop from the worn bush, it only about 60%, it still seems to accelerate well, but its totally unacceptable, so I will have to interpose a pivoting lever that translates the 30mm movement of throttle to 15mm of kickdown travel.
I have a plan, hope it works
I think I have cracked the problem of unequal travel between the throttle cable and BW8 kickdown cable.
The kickdown cable travel must be perfect, it is ridiculously sensitive to improper adjustment, we are talking 1mm !
The throttle travel is less critical, excepting the butterflies must always shut fully, however , I want my butterflies to sync closely to the trans cable position, and open 100%
The situation was the butterflies were not fully opening at WOT
Question @wiggles and others, I scarcely noticed butterflies opening ~75%
Should I expect a noticeable improvement in power with 100% opening, or is that last 25% not really an issue until high RPM ?
Anyway, here are crude paint drawings of what I came up with, and its 90% done, looks like it will work
The idea is to translate the 31mm throttle cable travel to the 11mm kickdown cable travel, in a linear fashion, and the pivoting intermediate lever should do this if my calculations are perfect.
Its all very tight in there.
I have to drill the final hole in the intermediate lever to pin the kickdown cable conrod
If I get it wrong, the new part is just sheet metal, so I cut another, till it’s perfect
When it is perfect, I have to go Hi Tensile, and buy a 1/2" longer coarse thread bolt to accept a stronger pivot lever.
I have made no alterations to the original Jaguar Parts that are in there.
keeping my fingers crossed for a test drive in the next few days
A more elegant solution may involve cams, and please, by all means make any suggestions, I believe the Mangosletti? design uses cams, I could not find a good pic, but will look again.
If mine works perfectly, I will be happy, as its dead simple, and cost exactly zero
(except I will have to buy one small bolt 
)
The engine can only use so much air, when you push the pedal more going uphill in a higher gear it will not do much more after it gets all the air it can consume, so logically you will only notice it during maximum power; and the first degrees make an enormous difference while the last degrees before fully open will make little difference to the total area of the airflow. So I don’t think it matters much but why would you like triple carbs if not to get the last few percent.
I understand youre asking if the carbs can supply all the air the engine can consume while only 75% open.
I heard somewhere that the triple SU are not nearly at the limit with the XK?
Well, David has pretty much covered all the points I was going to make… 
Especially on an automatic car, that last 25% is really not gonna make much difference within the normal driving range of that set-up. And yes, the kickdown/modulator cable is pretty sensitive to being set correctly.
Thats what I thought gents, although it should help at WOT, near max torque
kind of makes a mockery of “bored throttle bodies” and the like, which I have never been a fan of, unless there is some engineered restriction in the input
I have the twin manual choke HS8 on a S2 XJ engine, but I had to get the throttle right before moving on to fitting the triples, which look great, but any mechanical problems whatsoever manifest themselves more so in a triple carb setup.
Its not an upgrade unless its reliable
The original 420G throttle set up via rods is complicated, and I hope not to return to it
Theoretically: how often do you actually get there in a car with an automatic?
I think it is not around max torque but near and especially beyond maximum hp, because that is where the engine begins to run out of air, but there’s so many factors to consider; especially the head. Bigger intakes usually increase max hp and max useful rpm since the engine doesn’t run out of air as fast. Small intakes make good torque, too.
Also, max hp is where fuel consumption (and thus air consumption!) are at their highest, not max torque. That is where I see larger throats make a difference, I could be mistaken.
Anytime I press my foot fully to the floor (and hold it)
Most, if not all autos I drive will run near to the redline before changing, if I use WOT
It may not be an E-type, but it still wants to go sometimes
I can only assume, should this be true, that you have drawn a pentagram around your car and are conducting blood sacrifices within it.
None of the Jaguar throttle/kickdown linkages can be understood by mere humans.
