I've made a few shims out of that hard clear packing, it seems to be about 0.010" and its hard and flat, very handy!

FYI Carburettor is a Weber 34ICH and I understand that the return spring is often not strong enough for a braided choke cable and that is what caused the issue with it sticking. I fitted a push pull cable https://www.carbuildersolutions.com/uk/uncovered-push-pull-cable-6ft-long and this has sorted the problem