On Oct 17, 3:01*pm, "Peter Dohm" wrote:
"a" wrote in message

... Next time you're at altitude and in cruise mode, switch from 'both' to
a single bank of spark plugs. It will remind you what happens should
you have one side decide to go in/op when in flight. I had the engine
(IO 360) go rough a couple of weeks ago, but rough was a lot better
than the very smooth and silent effects the left mag only gave me.

Sounds like at least two problems--unless the fault was in the switch.

Peter
Just a thought

Nope. Engine went rough, stayed just as rough on the right bank, too
quiet on the left. After the repair all was well
again.

Even on run up you lose some RPMs when on a single bank of spark
plugs.