After further investigation, the rear carb' choke isn't responding from a cold start. The front choke immediately opens partially when the engine fires then gradually opens fully after around 5 minutes. The rear carb' choke flap doesn't move however when opened manually in time with the front carb' the engine runs fine. I have removed the cover and have continuity to earth from the feed terminal to the end of the heating element, although initially I couldn't achieve continuity therefore I am still a bit suspicious that the element may have a break that I have disturbed by poking with the probes and have now temporarily re-established connection. Anyway my question is, what is the interaction between the electrical heating and water heating of the bi-metallic spring ?. Is the electrical supply cut off when the coolant achieves normal temperature, triggered by the temperature switch in the manifold and thereafter the chokes are held open solely due to the coolant temperature ?. I expect the rear choke would open eventually as coolant temperature rises but until then it will be running over rich. I'm guessing it will be difficult to source a choke cover, although there must be plenty lying around having been swapped out with Webbers ?
After further investigation, the rear carb' choke isn't responding from a cold start. The front choke immediately opens partially when the engine fires then gradually opens fully after around 5 minutes. The rear carb' choke flap doesn't move however when opened manually in time with the front carb' the engine runs fine.
Here is your problem, if it does not open at the begining, it has nothing to do with the solenoid heating element, you must find cause in lack of vacuum (unlikely), stuck elements (probably) broken triangular membrane (probable)
I have removed the cover and have continuity to earth from the feed terminal to the end of the heating element, although initially I couldn't achieve continuity therefore I am still a bit suspicious that the element may have a break that I have disturbed by poking with the probes and have now temporarily re-established connection. Anyway my question is, what is the interaction between the electrical heating and water heating of the bi-metallic spring ?.
My assumption is electric heater is not that relevant in mild climates, IMHO, the electric heater help the coolant that is principal actor
Is the electrical supply cut off when the coolant achieves normal temperature, triggered by the temperature switch in the manifold and thereafter the chokes are held open solely due to the coolant temperature ?.
Not in my setup, but I learnt that there is a relayed version which I assumes might be yours with the temp sensor present behind the front manifold cover, you should have a relay in the brake booster arm
I expect the rear choke would open eventually as coolant temperature rises but until then it will be running over rich. I'm guessing it will be difficult to source a choke cover, although there must be plenty lying around having been swapped out with Webbers ?
Yeah, plenty of those swapped ones laying around, just in the same condition as yours
IMHO you should clean, overhaul and reset those carbs, once in a 40 years time is due.