first of all, congratulations to such a long-time serving and unmolested car! Then again, your tale leaves a string of mysteries behind:
Who put on the AED the wrong way - how would that work anyhow? How on earth do you “lose parts” from inside the AED (can’t open your link either)? Finally, if the AED is still on the car, how come you talk about “the car always needed the choke on for an excessive amount of time”, as there is no perceptible indicator when the bimetallic strip in the AED fully shuts of the aux carb? Frankie’s reply indicates he understands your comment just the way I do.
Maybe, you help us out with a description of your setup: I was under the impression that the DS420 in 1981 had the same engine setup as the XJ6 SIII and am surprised you’re talking about carbs in the first place. Maybe I’m just ignorant and the Daimler limos used the SII setup.
If this is the case, then what exactly do you mean by “needed the choke”? No stock XJ SI or II car had a simple “choke” fattening the mixture and part-opening the throttle on the main carbs. Instead, they all had either an Automatic Starting Device (ASD) or an Automatic Enrichment Device (AED) added upon the main carbs during cold start and cold running.
In particular, the AED used on SII cars consists of an auxiliary carburetter sitting between the (main) carbs and feeding a richer mixture into the intakes. This auxiliary carburetter is located in the lower part of the unit, while the upper part, hidden behind a black bakelite cover, houses the control of this aux carb, in particular a bimetallic strip operating the air and the fuel valve of the aux carb.
This AED, to function properly, needs hot air to make the bimetallic strip shut off properly when the engine has reached operation temperature. Hot air is guided from underneath the heat shield covering the exhaust manifold around the rear end of the engin in a foam insulated tube. Once the foam insulation has deteriorated the AED won’t work any more. The bimetallic strip has a tendency to fatigue over time. All in all, the control part of the aux part is mostly considered costly to replace every couple of years and cumbersome for classic car driving habits…
Most owners have replaced the control part of the AED with a manually operated camshaft replacing the bimetallic strip. This camshaft is sold as a kit by most parts suppliers, as Frankie mentioned. If mounted correctly it will solve most of your problems.
75 XJ6L 4.2 auto (UK spec)