Hmm, did you check that when the pedal's down you really get full throttle at the carb. end?

Delightfully I've bought both an older diesel vehicle and 2cvs with that problem in the past.

Interestingly, not just Citroens that suffer - I had a Sierra from new in circa 1986 which, due to the design of the cable clips/stops, meant that in the original position about 1/3 of the usable carb opening wasn't available - ended up re-routing the cable and all of a sudden massive more power.....

Roy,
is that problem with those carburettors which have been subjected to too much tension on the throttle cable, after which the 'full throttle' stop ( formed of mazak/monkey metal) has become so indented that the butterflies will go past the vertical position?

Once that's happened, it's either 'ease back slightly on the pedal for full steam ahead' or 'fix that stop'...

Or if someone has been heavy footed, the pedal gets bent down so it hits the floor before full throttle........

Trust me, it's the carburettor end which suffers most.
I've even known throttle pedals to have been bent upwards to 'give more travel and ensure full throttle', which makes matters even worse...

Just referring to adjustment at the carb end, at the plastic adjustment ferrule, positioning of the circlip.

Surprised nobody has suggested checking the ignition timing. As Dennis points out: "It starts very easily when cold" and "It smells a bit hot when I stop after putting my foot down..." Slightly too retarded perhaps?

my 2l HDI has that - well there isnt a throttle as such just a potentomiter gizmo bolted to an engine support - the poorly adjusted (from factory) "Throttle" cable was suspiciously familiar and it now tops out at over 90 as opposed to running out of steam at 2cv speeds

+1
go for the full "2468" rule

Tappets 0.25mm
points 0.45mm
plugs 0.65mm
timed to 8* ( peg in hole static)

should run ok after that then if not condensor, coil, leads before checking the fuel system,

We bought a Dyane some years ago that was hardly ever driven and then only very slowly we bought it from a lady who had owned it from new It was very sluggish on its first long trip to Greece, only just able to get to 70mph. By the end of the trip it was much quicker and more responsive. Could this engine just need to be "thrashed" a bit should I say allowed to rev.