Generally speaking, 4" of vacuum is sufficient to drive modern gyros,
and a properly functioning DG shouldn't precess any more than 5 degrees
every 15 minutes (which is a high rate of precession, but that's
apparently the number manufacturers use to determine warranty coverage).

Thanks, Doug (and everyone). We flew a couple of hours today, and the
vacuum is now consistently at 5.1.

I timed the precession of the DG in level flight, and it was five degrees
every 30 minutes -- MUCH better than before.

Of course, the temperature here was near 60 today -- about 45 degrees warmer
than when we noted the high precession rate. Did that have more to do with
it than the increased vacuum? Everything works better when it's warm, of
course.

I dunno. But it's good to have the problem licked, for now.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"