Ignition switch, what happen when Left or Right is selected

Yes. At idle. And I should have added that if it starts to
shudder and
die don't turn it back on.

It WILL start to shudder and die if you turn it off, unless there's a
bad P-lead connection or mag switch. You want it back on so you can
shut the engine off with mixture, not ignition.
I get really annoyed when students go to "Off" during the runup
and mag testing. We try to get them to hold the key firmly, not by its
edges, so that it won't inadvertently snap over to "Off" when they
select "R." They almost always immediately turn it on again (instead of
letting it spool to a stop and restarting) and the exhaust makes an
almighty BANG and I have to look closely at that muffler and piping
during inspections to find the cracks that often result.
That was the big joke when we were young, right? Turn of the
auto's ignition and back on again to get the big boom from the exhaust
system. Doesn't work anymore with fuel injection. Saves exhaust
systems, no doubt.

Dan