Okay, after looking at all the replies, you need to stop and analyze
the info given to you on the instrument. If there was a bad plug,
when he switched mags, (he should have leaned it out), the temps would
drop because there was no fire. Same with any other ignition part.
If there was no fuel getting to the chamber, same thing. What you're
seeing is a bad valve, probably exhaust.

How could a bad valve on #2 work okay on "both" mags -- but not on the left
mag?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"