Start-up problems 1963 E-type with triple SU HD8 carburettors

Hi guys,

I have after many trial and errors found out why car went too rich after overhaul, it appeared that the carbs had HD6 needles, not the thicker and longer HD8 needles. Found the original ones, some UO marked needles, some say UM, or UD or UE is better. So new needles are ordered.
The carburettors have been cleaned and overhauled by experts… Company closed down.

So car now start, no excessive fuel, but it goes direct to 2.500 to 3.000 rpm. Have checked with some Jaguar friends here in Norway and suggestion is false air or throttle butterfly installed the wrong way round.

I have also retightened all nuts to cylinder head and all nuts sitting on top of the inlet manifold binding these three lovely carbs together, have readjusted nozzles so all are aligned, readjusted idling screws etc.

I have also rechecked that the throttle butterifles are closing properly and they based on what I can see, they do close properly, but it is difficult to see whether throttle butterfly is installed the correct direction. I really cannot see that is causing this, 3.000 rpm then a lot of air has to pass through.

I have soaked all gaskets in oil prior to installation of carburettor system, to make certain no false air is the problem. Maybe I have had not enough oil on them?

I blocked the servo brake connection.

After all this, engine still goes crazy, 2.500 to 3.000 rpm, but not more unless I push the accelerator pedal/linkage system. Then it goes up and down like it should, but never less than 2.500 rpm.

Could it be ignition timing incorrect?

I am really stuck here. Some improvement it has been though with correct needles… :wink:

I would disconnect all three drop links so that the carburetors are not connected to the throttle linkage. Then start the engine to see what the idle is and make sure that each carburetor is closing its throttle plate completely at idle.

If it still is idling fast then you need to look for a vacuum leak or false air. You can do this by spraying carburetor cleaner on suspected leak areas which will change the RPM when you find the leak area.

Thanks, will go out and try right away. :grinning:

Hi again,

Disconnected links,had adjusted idling screws to zero.

What was discovered was, while the two front carbs pistons moved up and both reacted when pushing dampers a little up, while the rear carb damper/piston was completely dead. i also forced that up, but nothing really happened. so, any ideas where to move from here? it seems maybe it lacked some fuel?

idle speed still in the region just below 3.000 rpm. or is this a sign of a badly vacuum leak on the rear carburettor?

Now working. Thanks for your advice. Found out a smaller vacuum leak on rear inlet manifold part, ie connection of servo brakes. Rectified.

Then I found on the web a great recipee of how to tune a HD8 carb system. One little detail, like setting fast idle screw on 0 made the trick. and now all carbs are aligned, will run in the engine and then fine tune everything.

Car is coming alive again after two and a half year off the road. :slight_smile:

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Amazing what a little vacuum leak will do.

I recommend famous Ray Livingston’s carb adjustment guide. Just Google it.

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Yes Tom, interesting, vacuum leak, so high engine rpm. I will do remind it when I put everything together in my 3.8L car.
Frank.