I just spent 4 hours of mechanic time up at Lasar. At my request they went
through everything. Checked the tanks for water, checked the gas collator,
servo, injectors, spark plugs, exhaust for blockage, air intakes (filter,
alternate air, ram air) all without finding anything. Test flight afterward
and the flight home both had the engine running perfectly as if nothing had
ever happened. Everybody is scratching their heads a little but I'm pretty
sure the culprit was water in the tank. On the flight that I had the
trouble,
I made a step bank turn to stay under the fog ahead and I'm thinking there
was
some water trapped behind a rib in the wing. The steep turn could have
stirred it up and had it settle to the bottom of the tank, which then got
pulled into the engine. It ran really rough for a while as it was a mixture
(recently stirred up) of water and fuel and then when that mixture was all
pushed through, it cleared up and ran normal. Leaving no sign of what had
happened.

Lessons learned, 1) do not fly VFR Over the Top unless you absolutely have to

and if you do get a lot of altitude so you might have a chance to glide to a
clear area to land and 2) really work the wings and sump the tanks vigorously

after rain or even dense fog - or for that matter anytime before you go
flying
- you might have trapped water in the wing somewhere.

Thanks again to everybody who responded. I have learned a lot through this
experience.

Paul
Mooney M20F

Paul, you may want to think about that "steep bank to avoid fog ahead" comment.
It suggests

1: you may have been low,

2: if it stirred up the fuel tanks it may have been uncoordinated.

Man, if there's a nit to be picked. . .