On Jul 13, 3:33 pm, "Peter Dohm" wrote:

Aha!

I read your post this morning and didn't think much about it at the time;
but but it now occurs to me that the cooling air gains a lot of heat passing
through the cooling fins of the engine--so that you may have created your
own problem by sending cold outside air directly into the heat muff.

Just a thought.

Peter

And since those Aeronca muffs tend to leak a lot, forcing air into
them might cool the pipe too much just when the heat is needed. The OP
needs to seal up those muffs. The connection to the baffling needs to
stay, since a muffed pipe with no airflow (except when carb heat is
on) will overheat and burn out. Piper had plenty of that sort of
trouble on their Cherokees.

The OP gets a 50 RPM drop in cruise, with carb heat. That ain't
much.

Dan