Well, since the last post, I have done a fair bit of work on the car but seemingly got nowhere until yesterday.
The knocking under load was easily sorted, I had timing that was about 50% extra advanced over where it should have been. Cleaned up the points and reset that, but it looks as if the condensor is failing, there is quite a bit of sparking. I ordered a new condensor already, but on the plus side, I managed to find what is probably a period 80s points assist ignition system when I was clearing out the garage:
(Not my picture, but the same unit)
Assuming that works it will definitely be fitted, as the quality of modern condensors is notoriously poor.
Next unscheduled problem was carburettor related. As standard, the Solex in the 2CV was fitted with a 102 size primary jet. This was quite small, fitted by Citroen in order to lower emissions. On modern unleaded petrol, this tends to make the engine run a bit too lean, and causes a weakness at the peak of the first choke. This means you get a flat spot between the two chokes as they changeover.
The recommended modern fix for this is to fit a 107 jet, so I had ordered one of these. The intention of this is that it keeps enough fuel going in the primary to remove the flat spot, and give a bit more low down/mid-range poke. Problem is, I fitted it expecting great things, so I was pretty disappointed when I test drove it to suddenly find a huuuuge flat spot in the mid range. After putting the 102 back, same thing.
After fixing a few issues that were not the cause (split gaskets, cracked spacers, one gasket had burnt away) and trying another carburettor (this one wouldn't idle unless set to maximum rich, which causes it's own set of problems) I finally sorted it by letting it sit for a few hours full of carburettor cleaner, with everything removed that I could. After that, pleased to report the car now goes like hell (for a 2CV anyway) and definitely has more mid range punch.
Carb is a lot cleaner than the rest of the engine now.
First signs of issues. This is the carburettor mounting spacer.
This was the burnt gasket, I think this was due to the fact that the carb wasn't properly tightened down at the front. The nuts were finger tight when I came to take it off initially.
Next issue to sort is the growing oil leak, that I'm hoping is not pushrod seals.