Cub Driver wrote:

But the other day, first cold day, I had quite a different experience.
The engine may have been running rough when I taxied--hard to know
with earphones, but I had a feel it was rough. Did the mag check.
Pulled carb heat on. Whoom! Rpms went up to 1700.


The reason it zooms back to 1700 is that the ice melted and you were
giving it enough gas for 1700. The engine running rough on taxi is a
good indication of that, too. The rpms may have dropped momentarily,
but the ice release was apparently very sudden and it appeared to have
just gone up. Did the rpms increase again when you turned carb heat
off? They should have.