[wilf leek]

Sorry Buzz, I guess I should have asked for more info before jumping in. Is this "backfire" through the carb or is it an exhaust noise?
If the latter, are you sure it's not just an exhaust "blow" or leak somewhere? You should be able to feel the gasses coming out at the source if it was that bad.
If it is continuously backfiring throught the carb, then I would suspect a sticking inlet valve - a compression check should show up which cylinder it could be.
I wonder if the valve lash has been set too tight, holding a valve off its seat somewhere?
Sorry - you are going to have to pin this down before you run that engine too much more.
As for the electric choke - I should think that the missing connection would be a power feed through the ignition. Can't see that you are going to need a choke in your climate! I stripped mine completely off my own car here in the UK and don't miss it a bit.
I don't see this as part of your current problem, unless the thing is stuck in the cold start mode, and then you would have a very badly running engine, with lots of black smoke from the exhaust.