I will have to say that the cast iron single manifold, with or without
the secondary butterflies, is certainly more tractable on startup in
very cold weather. In fact my 122, with aluminum manifold, will be
crochety for the first 5 miles or so unless I crank it up, drive it a
couple blocks, then shut it down so the heat can conduct back to the
manifold and carbs. Otherwise the heat of evaporation of the gasoline
being taken out of the carbs and manifold continuously prevents them
from getting warm until the whole engine room is warm.

When I came back to Oklahoma I reinstalled the thermal flapper on the
air intake of my 164 so it pulled air from near the exhaust pipe and
it made a WORLD of difference in tractability on and shortly after
startup in very cold weather. It has the secondary butterflies removed,
btw.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma