If a 2cv carb is used on a 2cv engine with visa pistons I know it is probably more restrictive but as the revs get close to maximum will the mixture become more or less weaker

Kevin,
it may depend on which air filter is fitted.
The standard A series filter is reputed to be on the restrictive side at WOT/high rpm even for a 602 engine, but any enrichment of the mixture under those conditions is erring on the side of safety.
If you did find that it was going too rich at high rpm, I'd have thought it was easy enough to fine tune by fitting a slightly larger air corrector jet, as that would flatten out the slope of 'enrichment vs air velocity through the carb'.
Don't ask me which one, as it's been a long time since I've had a lambda sensor fitted to a road car...

ken

depends on so many things!-which 2cv carb? what exhaust and filter?
fixed choke carbs are fine when they are working in the application they were jetted for- but then it becomes a balancing act between the main jet and the "emulsion tube" and "air correction jet" when you start messing its very easy to loose the plot-then its put it all back to standard and start again.

id keep it standard and do a "plug chop" run it at wot for as long as possible ,clutch, kill engine coast to a stop and pull the plugs out for a look?

you could go down the lambda sensor route, various sensors,displays and homebrew stuff on the net.

2cv6 Solex 26/35 CSIC cit 225/226 carb, with a Citroen AX air filter:

Air correction jet 1st choke: 1F5
Main jet 1st choke: 110 or 120

Air correction jet 2nd choke: 2AB
Main jet 2nd choke: 120