Dick, I read your question as icing in non-carburettor engine air intake ducts. Have you been to
RRHT and looked at the history of icing in the Britannia intake ducts? Not a piston engine but a persistent sufferer from intake icing. There must be plenty of detailed reports available on those dusty shelves. Sorry if I've misunderstood and this is irrelevant.
PS - Lovely piece of Ernest K Gann, Brian.