New XK-140 Owner. Included H8 Carburetors

I am new to the XK adventure and have secured a fairly complete but non running 55 OTS with standard cylinder head (8:1 compression) and OD. There were extra parts, including a set of H8 carbs. They seem in excellent shape. I am curious about the date stampings. One has P3 (March 1957) and the other has N13 (another way of stating January 1957 ??). The sandcast piston bodies have been turned down with a lathe professionally (apparently when literally new) and smoothed. They look good, and I know the previous owner was a machinist and liked things looking “sharp”. Enclosed are a few pictures. Any comments would be welcomed.

Congratulations Ken! You won at least part of the lottery with that purchase. You will undoubtedly awaken the H8 gods with this post who have studied these carburetors closely. Here are just a few preliminary comments. First, the bad news. Your machinist owner should have kept his hands off these. The original sandcast finish is highly valued as the hallmark of these carbs and doing away with it will decrease their value. There are reproductions made by Burlen, but I think they are based on HD8s and cannot reliably be used as a source of replacement parts. You should check with Burlen to see if your machined parts can be replaced. Now, the good news. These carbs are still very cool and very rare. They look great and are a unique piece of 1950’s racing technology. I found them to be difficult, but not impossible, to set up properly. My car is not yet back on the road, but my hope is that they will work on the road as well as the track. My carbs also have the P3 stamp. I am not convinced that the letters strictly correspond to calendar years (though others are convinced) and your N13 stamp would seem to raise that question as well. Another possibility might be a production run rather than a calendar year. No SU factory documents survive to settle the issue definitively. In any event, these carbs appear to post date the manufacture of your car and were probably purchased by the original owner as an add on. Other items included in the factory install of H8s include a mechanical distributor, special mount for the coil, mechanical choke and cable, blanking plate over the otter switch mount point on the intake manifold, longer studs where the carbs bolt on, openings in intake manifold machined out to two inches, and a unique fuel intake line. Let us know if you car has any or all of these. If you are in contact with the original owner’s family, I would also pump them for all the information they might have. That is quite a find in a box of spare parts.

I’ve worked with dozens of machinists, and that attitude is very typical, they would often give me a micro finish much finer than I specified on my drawings. Smooth H-8s would not bother me at all. Welcome to the fun.

Actually, its quite common for H8s to be POLISHED to various stages of smoothness, fully turned down like these is not so common…

Indeed I have just finished restoring a pair of genuine C-type H8 carburetters - in detail different from later XK140 version, and indeed also aftermarket Spare Parts H8s which these two are - P3 and N13 date codes advise. But my biggest challenge was how to recover their ‘polished’ suction chambers and fuel bowls…
Fortunately, some excellent advice leading to two incredibly skilled specialists in Melbourne, have resulted in my successful restoration of their original sand cast appearance/texture surface finish where I had a NOS example to faithfully copy, only thing is the aluminium now looks freshly cast/new, so I might have to age/weather them a little…

And by the way, BURLEN do supply good quality/accurate INTERNAL components for H8 restoration, but you still have to know exactly what parts you actually need as Burlen tends to only supply the latest parts supersession from the 1960s/70s, and not necessarily authentic 1952-56 parts, noting as above, that there are also a number of differences 1952 to 1956 originally anyway…
But what lets down the Burlen parts is the appearance/surface finish/accuracy of all their cast aluminium parts - so all the visible bits - Suction Chamber, Fuel Bowl and Body (all sand cast) and the Fuel Bowl lid (pressure die cast) - but appearance/authenticity aside, they do actually function well, or at least as well as the originals did - which is not great at low revs and general road use…

Thanks for the comments ! It looks like the H8 carbs were never put on my car. None of the needed modified components are present and the H6 set on the engine match the correct “predate” of the manufacture date of the car. It looks like these carbs were an uncompleted project 60 years ago.
Roger, that picture looks like you have a very high carb diet ! It looks like auto jewelry. I may have to do some alchemy and change my set into other Jaguar parts.

Welcome Ken

Do you have more pictures of your H8s?

I have a pair that are a little later than yours (T8) and would be keen to know if the finish of some of the steel parts on your unrestored pair are either unfinished or black oxide. The jet links, fuel chamber support strap and nut and the 8 suction chamber fixing screws and shake proof washers.

These steel parts on my unrestored (but needing restoration) carbs are all unfinished and if yours are too I think this would confirm they were originally unfinished. On earlier H8s they were black oxide.

Many thanks

Here are a few pictures of the parts in question on my H8 examples. It appears the chamber support stays were black oxide as well as all the chamber screw washers (the only washer not black oxide is the brass one noted in the first 2 pictures).One set of chamber screws are bare, the other is black oxide- how is that for splitting the issue down the middle! (the P3 labeled carb has the black oxide screws). The float bowl top screw is brass and the support stay screw on the carb body is black oxide. The jet links were bare brass, fixed portion of levers were black oxide, movable portions of levers bare brass, return spring was black oxide and jet link compression spring appears bare. The throttle couplings and anchors are bare. The vacuum connection is brass. The fuel line/rail is totally cadmium plated . I hope that helps .

Good pics and detail Ken,

Your fuel line is of course for standard twin H6 carburetters - the special fuel line for H8s is quite different… see attached, unfortunately stripped under restoration, and not yet replated…, but the shape/size is 100%

I was wondering why the line did not look like it would fit! It was initially connected to one of the carbs.
Thanks for the picture.

Ken, Many thanks for the good photos.

Interesting how the black oxide chips off and gives no indication of ever being applied.

The H8s I own, and others I have seen, have jet link levers with no trace of black oxide, not even in the darkest corners, so I assume they were never treated.

The period SU parts catalogues list the link lever finish for some cars as being dull nickel. I will assume the finish on my parts is therefore dull nickel and original.

Thanks again

Hello. I have a little experience with black oxide coatings. BO is a chemical process an actually impregnates the surface of the base material. BO is not a rust proofing coating. It will rust. The pictures show black paint peeling or chipping off the base part. BO can not chip off. The parts in question have not been BO but painted I believe

When was BO invented? I’ll have to investigate

Can one do a black oxide finish at home - what is the process?

I’ve used Caswell Plating over the years. They sell home plating kits and chemicals including the black oxide chemical dip. Their user manual is very extensive