Matt Whiting wrote...

...but he may be referring to turning on the carb heat
after he's already accumulated enough carb ice to noticeably
decrease his RPM.

Yeah, that's it. g No, I'm afraid UltraJohn was right.
I haven't seen anything remotely resembling carb ice,
and from what I've heard it's not very common in RVs.
I get a very slight RPM *drop* with carb heat, presumably
to a slight temperature *rise* from switching to undercowl
air.

Dave 'cold throat' Hyde

"My wallet's fat and so is my head" - Greenday, 'Walking Contradiction