The motor won't stop turning all the time you are flying well above Vs. Too much airflow.
To stop an engine (that is not mechanically broken) you have to pitch up aggressively (maybe 30 degrees up) and switch off the ignition / close the mixture.
I was in a C150 with an instructor who did it for fun. I also know somebody who flew with the same instructor who did it at 2000ft
IMHO if an engine stops turning, in any kind of normal flight, it is gone.