Greg,

All the explanations you got are good. Now for the carb heat check.
What happens to the EGTs?

FWIW, a while ago I had a too high RPM drop on the mag check with our
Lyc O-360. A look at the engine monitor showed one cylinder's EGT going
very high. This points strongly to one plug being fouled. A little time
of running the engine at high rpm and very lean on the ground cleared
the problem, which could also clearly be seen on the engine monitor.
These things are worth their weight in gold, even on the simpler
engines.

--
Thomas Borchert (EDDH)