This might help.

My nephew works for one of the large motoring organisations acting as customer technical support for a major car maker. (Sorry can't say who). He receives daily complaints about one of their engines hesitating at certain throttle openings with poor engine response. Seems to "baffle" the ECU.

The car is sold all over the world but he tells me the problem seems to be exclusive to UK. If you cross the channel and fill up with French fuel the problem instantly goes away.

Which tends to Back up Steve Hills theory !!

"Spoke with Steve about it and he said I was not the first 2CV that he has seen with the same problem (a Lady client driving from reading to him approx same distance from a similar area had the same problem which he put down to bad fuel in our area???)"

As he has not had the same problem in France!!

All makes complete sense
So I'm advanced by 2 teeth
Thanks Sean

thats why its advised over here by "those who know" to use a strobe to set the advance to a maximum, increase the primary jet size and to use NGK 7s or even 8s and even increase the tappet clearance exhaust side.

wheras in France you can stick magnets on the pipe send it round a curly bit of steel time it to the peg use electronic iggy etc etc and unless you have it set wildly wrong it wont pink and therefore the aforementioned gadgets work and us Rostbifs are all barking up the wrong tree

pennies starting to drop

That's very interesting. I've overhauled my carb with an ECAS kit, checked for air leaks, fitted 123Ignition, new B6 plugs, adjusted valve clearances (well on only one side yet ) and I've still got real hesitation at low throttle openings. Yet it goes like the clappers when the second choke opens.

Is it common to need to play with jet sizes then?

Sounds like I need to fill up with some UK fuel, pop on the chunnel and pay you a visit!!!

emu_p,
interesting, wonder if this fellow has any other suggestions for damaging customers' engines?

One of the principal requirements for setting up an engine is that it should not pink/knock under any condition of use.
Even on modern engines with their sophisticated engine management systems, the relatively simple knock sensor's function is to retard the ignition timing immediately any hint of knocking is detected.

Timing which is over-advanced may 'seem' to produce more power, but it's not usable power unless you are willing to run the risk of engine damage...

ken.

I've just been gifted a strobe, shall have a play

I'd really like to know if other jet sizes would solve my problem if anyone can help thanks

It's only one jet which needs changing.
Increasing the primary petrol jet from 102.5 to 107.5 eliminates the weak mixture on the first choke, then the transition between first choke to both chokes is barely noticeable.

ken.