Mike:
After a fresh look at these discussions (and also a peek at
CAA Safety Sense Leaflet 14A "Piston Engine Icing" I now agree with you on the venturi aspect.
The SSL in fact I believe is misleading, in that it does not IMHO adequately explain the nature of the pressure drop at low throttle settings:
It quotes:
"The most common [type]...is carb icing
caused by the sudden temperature
drop due to fuel vaporisation and
pressure reduction at the carburettor
venturi."
and
"ice which gradually blocks the venturi."
and
"Engines at reduced power settings
are more prone to icing because
engine induction temperatures are
lower. Also, the partially closed
butterfly can more easily be
restricted by the ice build-up."
There is no mention of the greatest pressure drop being caused by the butterfly itself.
What is your opinion of the accuracy of the SSL info?
DT