I hesitate to ask this (no pun intended but it's quite good actually) but I do have a bit of a flat spot that's always been there. It's been so long I'm not sure if it's just normal.

I only recently read on here that the idle mixture is different to the main mixture? Carburettors have always seemed mysterious to me so I apologise for the dunce questions.
A year or so ago I did get the larger jet from Ecas (107 is it?) and while the guy was doing my kingpins I asked him to fit that jet. It did improve matters as I had a hesitation at part throttle. He also checked the float level for me, and said it was 'all over the place'. I replaced the spacer block thing which was indeed cracked in an unseen place as they apparently do.

The car starts on the button in any weather and is lovely to drive really despite this flat spot. When it's cold though the flat spot is huuuuuuuge ☺

I'm just wondering how I would go about maybe setting the mixture. (Or getting someone else to properly.) The chap who fitted the jet cocked everything else up tbh, so I'm thinking there may be improvements to be had with adjustment.

Idle mixture was adjusted at MOT time and is within spec for the test. I actually had no idea it was separate.
I'd happily take it somewhere to have it set accurately but can't imagine anyone knowing how to do it these days. Sadly my 2cv garage is no longer really a 2cv garage since the resident expert retired.

If someone can answer Ian's question, perhaps they could include an explanation of the primary and secondary jets - old carbs only had one main jet. And isn't the idle jet something different from both?

I found this useful .....Google search " 2cv carburettor tuning"

Dennis,
I guess that when you mentioned 'old' carburettors, you were referring to the single choke type?
Since each choke (aka venturi) of a carburettor needs a main jet, that's why twin choke carburettors have two main jets, also two emulsion tubes and two air corrector jets.
With all 'fixed jet' carburettors, the idle circuit is separate from the main circuit(s), with its own (small) petrol jet.

Thanks Pete. Been looking around on google already for info but thought I'd see if anyone here had suggestions.

As luck would have it, I bumped into Mr Ex Mechanic (retired) from the garage and he said he'd have a look after Xmas. And maybe there's some dirt blocking a jet or something.

I'll update this thread if/when it happens.