Just completed the latest Solex 40Pl rebuild. These carbs are reasonably tricky to restore as the internal ball valves that control the accelerator pumps and the vacuum operated high speed enrichment circuit are quite commonly blocked and don't operate correctly.
We replace the lower ball valves clean out all the internal galleries, remove, clean and replace the upper ball, replace throttle shafts, throttle valves and re-bush the spindles.
The accelerator pumps are set and matched and the internal floats are set to have the same height.
Another common problem is the shaft that controls the accelerator pump lever wears and causes uneven pump operation.
We have made new shafts and always replace the old shafts as a matter of routine.
The repair kits available for these carbs are quite variable and we now make all our own gaskets, diaphragms and spring sets as well as idle mixture screws and pump actuation rods as these parts are often damaged or badly corroded.