I could only find one or two images on the net of this carb (evidently
fitted to Renault cars among others). From what I can tell, it seems
that like other Solex carbs, the throttle shaft goes through the alloy
casting. A steel rotating shaft in a hole drilled through an aluminum
alloy casting is just a disaster. This till wear causing vacuum leaks,
and Solex has known about this for decades. With the carb's throttle
cable disconnected and the return spring removed, wiggle the shaft. If
it moses sideways r up and down then it is a major cause for vacuum
leaks. If the shaft is not factory equipped with an O ring seal (like
on some Bing carbs) then the carb needs to be repaired or replaced.
This is more cirtical the newer the car is- the reason is that the
addition of pollution controls and low manifold vac at idle makes
these leaks really serious as far as trying to get the car adjusted
properly.

If that is the case, you may be able to find a machine shop to drill
out the carb body and install bronze oilite bushings to remedy the
problem. if not, you may be able to create a short-term seal in some
way.  Good luck...
            __  __
    Randy & \ \/ /alerie's
             \__/olvos
'90 245 Estate  -  '93 965 Estate
  "Shelby"     &      "Kate"