Posted for "Bob Jude" <bobjude@charter.net>:

Lorn
I struggled with that problem for a long time also and didn't make much of
an improvement.  I tried to force more air through the muff by installing an
air scoop near the inlet.  That actually made the situation worse. I had a
couple of  SS baffles welded inside the heat muff so as to increase the path
length of the air flow which did help a little.  Also, I wrapped the heat
muff with fibrafax insulation.
After flying for a couple of years and watching the carburetor air
temperature gage, I decided that I could live with the situation, as is.  I
also have a O 320-D1F, normally aspirated.  As you know, the carb. is
mounted on the bottom of the oil sump and the hot oil significantly reduces
the potential for formation of carb. ice, as compared to say, a Continental
engine.  I have been flying it for 7 years and have not had a problem.  When
humidity and temperature conditions are conducive to formation of carb ice.
I just watch the carb. air temperature gage very closely.  If it should move
down into the yellow range, I would change my plans.  But it never has.  You
do have a carb. air temperature gage, don't you.
Bob Jude
N65BJ