SU H6 (XK140) questions

XK
1

Through the water pump / thermostat cooling system rebuild, past the Distributor rebuild (unplanned), now on to the carb hopefully adjustments (also unplanned!) one day maybe I’ll get to drive this car!

I found that after servicing the distributor the car seemed to be running rich, ie almost stalling when the throttle is first blipped once warmed up, and the plugs looking very black very quickly. She also has a bit of a lumpy idle.

So I figured a quick carb adjustment was called for.

The rear carb seems pretty good - clean, nice drop to the piston, found the jet adjustment screw to be 2 turns out which seems like it might actually be a bit lean as I believe the starting point is 2.5 turns?

The front carb is a bit of a mystery… slightly different looking piston which set of some alarms in my head, and not a sharp drop to the bridge. My plan was to try and recenter the jet on this carb, and then set idle and mixture on both and see where that got me against my stalling / stuttering issue.

So i was surprised to find that the font carb does not have the cap on the bottom of the jet adjuster. Anyways, not sure how long it has been missing, but I decided to proceed with my plan and order up a new Cap to install as some point in the hopefully not to distant future, in the meantime I was hoping that I could still adjust the carbs and drive the car without this piece.

I proceeded to screw the jet adjusting screw up to see how many turns it was currently set at vs the front one at 2. But it seems that the Nut that secures the jet assembly is turning as well and after many many turns I am failing to understand the relationship of the jet assembly parts… I’d like to have a sense of what the assembly procedure is for these parts so I can understand how to correctly set them up from here… I have not taken these parts out of the carb body and would prefer not to - the carbs are still on the engine and if I proceed much further then I guess I’m looking at doing a complete rebuild - not really what I wanted to do right now although I can see it coming maybe this winter.

So has anyone got reassembly instructions for the jet assembly on the H6 that would help me understand how to adjust jet bearing and securing nut,

and also, is it OK to drive the car without the Cap on the bottom of the jet adjuster screw? interesting that when I pulled this cap off the rear carb it was full of gas - if that’s normal then the front carb should be leaking without its cap, but I haven’t noticed any gas leaks… one of the first things I checked for when I first took on this car!

Cheers,

2

I would not drive without the cap.
On both my carb’s there is always fuel leaking in the Cap, looks to be normal.
The reassembly of the jets is just a matter of feeling, but always with the piston and needle in place.
And the piston as low as possible.

Regards,
Peter Jan

3

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In proper shape with the 48 cap and 46 seal they do not leak.
Agreeing with Peter, if it is not leaking without the cap, the 44-47 jet assy is likely gummed up with gook.

4

Cap #1661 (D48) in the parts book has a red fiber washer inside it. There is no listing for it in the book. #5536 (D46) is a copper washer at the top of 1656 (D44). Cap will still leak if it does not have the correct fiber washer inside. Curto or Burien probably can supply.

5

One day I noticed that the tiny red fiber sealing washer inside the cap on the bottom of one of the carbs on my 140 was missing.
So I decided to make a washer out of a thin sheet of gasket material. It was not easy, the difference between the inside diameter and the outside diameter of the washer is tiny.
So, with the newly made sealing washer positioned on the tiny ledge inside the cap, I replaced the cap onto the bottom of the carb, and proudly started up the engine. It was now suddenly running very lean on that carb.
So I took off that cap, and the engine now ran normally.
So I put the cap back on, and again, that carb ran very lean.

Turns out, I had inadvertently made the inside diameter of the homemade washer slightly too small, and the inside circumference of the washer was rubbing on the head of the mixture screw, causing the mixture screw to turn inward (causing the leanness) with the cap as I tightened the cap.
When I unscrewed the cap to remove it, the mixture screw screwed itself back out, returning to its correct position.

Lesson learned: if you try to make one of the tiny sealing washers yourself, make sure it’s inner diameter is large enough to not contact the head of the mixture screw.

6

Ah, yes, the 1660 (3159) fiber washer is missing from the “D” parts list, but it is on the “AD” parts list.
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I too made the mistake in my younger days of using a fiber washer from the local hardware store and it caught on the cheese head jet adjuster screw.
The correct washer is available from Moss Motors and others.

7

I have replaced the little cork seals around the jet area for fuel resistant rubber seals.
Modern fuels will eat the cork. ( I only use ron 98 fuel, as it contains no alcohol here)

8

Peter:

Interesting that you say that modern fuels will eat the cork. I replaced my cork seals many years ago, prior to ethanol usage, and was advised by the chap who sold them to me to soak them in oil overnight before installation. I did and have not experienced any problems. You are right, the caps below the mixture adjusting screw always have fuel in them whenever I have removed them.

Chris.

9

thanks for all the input! got her back on the road today, post cooling system over-haul, post distributor service, and finally post carbs… lots of different service piling up on top of each other which had me concerned, I generally like to fix one thing at a time so when the test drive happens you know what to watch for!
The carbs got a very rudimentary check-over and adjustment. When I wrote the early questions I was hung up on the design / assembly of the jet components as it was all still in the car and therefore hard to see, and I didn’t want to dismantle any further than necessary and risk loosing parts etc into the engine compartment. As it turns out I ended up taking the jet assembly out of the front carb by accident! I thought there might be more threads on the retaining nut… once out everything became clear, and it was pretty quick to get it back together; I centered the jets on both carbs, re-synced them, reset the idle and the mixture; all came together pretty fast. the front carb is still missing the bottom cap but is not leaking; so part will be on order but seems ok in the short term.
Interesting that I can’t get the revs down below @ 1200 rpm even when very warm and the throttle screws all the way out… maybe the throttle plates aren’t closing fully? she was idling a bit lower before, but very lumpy and hesitating - i suspect this was because the mixture screws where set too rich, definitely the plugs were always black, once she cools down from today’s drive which went very smoothly, I’ll pull a couple of plugs and inspect. Full carb rebuild on the planner for this winter…
Last issue to sort is a bit of run-on after killing the ignition… my timing light is broken so that may be a couple of days before I can sort that one out!

Cheers,

10

The run-on is definite sign of partially open throttle plates or vacuum leak somewhere else.

11

Hi Kris, I will be having a good look at the throttle plates, but if I don’t get results there, where would I look for vacuum leaks? Cheers,

12

Dave, check that the carb linkages are adjusted so when the throttle screws are backed all the way out the throttle plates are closing fully.

With the engine off, back out the throttle screw, then open the throttle and insert your thinnest feeler gauge under the throttle screw. Then close the throttle. If the throttle plate is closing fully, the feeler gauge will be gripped tightly. Repeat on the other carb.

If the feeler gauge isn’t gripped tightly on either or both carbs, then make appropriate adjustments to the carb linkages before attempting to tune the carbs.

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13

Your AED, has some fittings on bottom of intake manifold that may leak. AED solenoid valve seat in good shape? I would bet it is a carb throttle that is a bit too open causing the dieseling. I have a XK150 with vacuum ports for brake booster, don’t think you have that but just in case check for leaks there and for your windscreen washer. I spray WD40 around intake manifold gaskets to check for engine speed increase when looking for leaks. It has propane propellant that will increase rpm if sucked into manifold.

14

Mike, definitely not going to grip a feeler gauge, it takes @ 1.5 turns on the throttle screw from when it is flush with the underside of its lever until it contacts the body of the carb.
I have disconnected the linkage between the two carbs and between the rear carb and the links to the gas pedal so it is only each carbs return spring acting on each carb independently . I am loath to remove the carbs from the car… I know if I do it will be weeks before they go back on as I need to order parts, and once I start I don’t stop shy of a pretty complete rebuild… a little OCD … hoping to put that off until the winter!
I did loosen the nuts that mount the carbs on the manifold and moved the carbs a few mm away from the manifold. I then used a flashlight inside the carb body to check for light leaks behind the throttle plate while opening and closing it, when closed , with both carbs no light appeared to be leaking past the plates… Maybe not a good test?
I’m flying blind as I do not have any manuals on rebuilding these guys, so I don’t see how I can change the relationship between the throttle plates and the shafts and throttle screw mounts… I’ll look closer tomorrow, and hints would be appreciated! I know if I took them off it would become clear but still trying to avoid that…
I did notice a fair amount of play in the throttle shafts as they ride in the carb bodies… I wonder if the rebuild kits such as CRK240 as sold by Burlen and others includes bushing of some sort for this or if that is a more complicated job… again would be obvious if they where out of the car!
I will try spraying some wd40 around these shaft areas to see if that indicates a leak as per Kris’s recommendation and a valuable trick I’ve used when setting 4 carbs on old motorcycles!
And Kris, what is the AED?are you refering to the Starting / Thermocarb?

Thanks again!

15

Yes, Auxiliary Enrichment Device. Loose throttle shaft bushings could easily be your main problem. I see carb rebuilds in your future.

16

Had my spindles rebushed with new spindles and butterflies by Burlen Services and they did a great job. Idles at a rock steady 500rpm even when cold. It’s quite a complicated job which requires some precision. There is a YouTube video of Joe Curto doing the job in the US.