Sometimes carburators can freeze when the car has just started and the
engine is not fully heated up yet. A common problem with older cars is
that blow-by past the rings injects water vapour into the crankcase. If the
crankcase is vented to the carburator inlet you get this water
condensating and freezing in the carburator throat which may block the
jet and jam the piston. The solution is to vent the crankcase somewhere
else.
The reason the water condensates and freezes is the high air velocity
through the throat and the rapid change in air pressure from place to
place as air flows over the bridge. Of course, the problem gets worse as
the temperature drops and the relative humidity increases.
Dirk
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