"Marty from Sunny Florida" wrote in message
...
... We were at 6,800 feet, strait (sic) and level flight running
at 75% power (about 2350 RPM) ...

Peculiar cruising altitude, BTW (the glades aren't above
3800 feet, are they?) ...

when I got my pre-flight briefing, the temp was 26 and dew
point 16. It was unseasonably cool and very dry for Florida.
At altitude, I knew the air had almost no moisture,

With temp 26, dew point 16, there's definitely moisture
there. Cool that air down to 16, and you'll start to get
condensation.) At 6800 feet the OAT would have been
cooler and the spread less.

... My next move was carb heat, even though there was
absolutely no visible moisture.

NB: There is absolutely *no* requirement for 'visible
moisture' for carb ice to occur.

It did smooth out the roughness slightly, but did nothing
for the power loss. ...

As others have observed, this is entirely consistent with
carb icing, and (if you didn't (you didn't actually say)) you
should have left the carb heat on.

The unusual cold (for Florida) and the couple of planes
that had the same problem the day before would suggest
this as well. It's lookin' like Florida doesn't get enough
experience with carb icing. (I'm not criticising, just
jealous.))

But good job!, and good story.