"Jay Honeck" wrote in message news:Mplod.135318$R05.23672@attbi_s53...
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?

I think there's some confusion about your troubleshooting. In the
original post, I (possibly by mistake) assumed that when you switched
to the rough mag, the #2 EGT "shot off the scale" to the low end (i.e.
cold). If you're saying it shot off the high end of the scale, this
would not be the kind of reading you'd expect from a cylinder that is
not firing.

On the other hand, like you, I have a hard time imagining how a
stuck valve would behave differently by switching the mags. If an
exhaust valve is stuck open, your EGT should shoot upward off the
scale, but it shouldn't go back to normal by switching mags.

If the symptom is truly that the #2 EGT shoots up when switching to
the rough mag, then something isn't adding up.

John Galban=====N4BQ (PA28-180)