I have never seen any information on the internals of the Villiers centrepiece published anywhere….ever. Further to that, as the centrepiece is made in two parts and very tightly assembled, they went to great pains to tell people NOT to disassemble them so as to look at the internals. There is nothing to gain from doing so and every chance of creating problems for yourself if you do.
Over a long period the top hole of the centrepiece may be worn out of true by the working action of the taper needle. Slight wear may be compensated for by a change of needle but for the effort and time wasted to do this and get it right it is far easier to just simply fit a new centrepiece and be done with it.
Villiers may have altered the internal arrangements of the centrepiece several times over its lifetime. We don’t know, we have no way of finding out and does it really matter? Regardless of the internal arrangements the MW carb on your Mk XIIC still runs best with a number 2 centrepiece. That is all we need to know for successful operation.
