An update for the L527KWC file.
Mothering Sunday was the first proper outing of the year and the old girl (car) disgraced herself by resuming the difficult starting and eventual coughing and spluttering into life accompanied by loud pops and bangs that have been an on/off feature of the car over the years. All this with a car full of senior ladies outside a posh hotel so slightly embarrassing.
There is another current XJ81 thread where the car has starting problems and a possible cause - as with mine has been an air leak on the induction system. I decided to change the plug leads anyway as these were the originals and whilst at it have a thorough check of all the vacuum hoses.
Note the difference in thickness between the old and new ignition leads:
Checking the rubber blanking plugs under the inlet manifolds I found a mixed selection of rubber items in use. I think this is probably what they should be:
One was not sealing properly so lacking anything else I resorted to the short bit of hose with a bolt screwed in the end.
More significant was this hose under the A bank which feeds the auxiliary air valve and has a T off to the distributor:
The manifold end was only secured by a cable tie and was not air tight. Also there was this angle piece which does not look original and the thin pipe to the distributor was a length of fuel pipe.
This is where the t off joins the distributor, fiddly to get at.
I imagine that all these loose connections, although none were major leaks individually, added up to a significant loss of vacuum.
Anyway, it seems to have done the trick and now (fingers crossed) starts on the button.