A strange richness...

My guess, and it's just a guess, is that you flooded the primed cylinders
while the remaining cylinders fired and operated normally, thus the
roughness.

As you advanced the mixture, the primed cylinders continued to be flooded
but the non-primed cylinders operated normally, albeit at a possibly rich
mixture.

As you retarded the mixture, the primed cylinders were then able to
completely burn the leaner mixture and clean themselves up.

Jim

"Jay Honeck" wrote in message
oups.com...
You "primed a few pumps", I take it this means throttle pumping
(accelerator
pumps?) on an already hot engine? I'd guess you did over prime and then
flood the engine.. I am not sure of your engine but I presume it is also
an
IO-540?

Nope. Pumped the primer a couple of times. (The little
Coleman-lantern-style-thingie)

The engine is a normally-aspirated O-540.

I obviously flooded it, but I don't quite understand how this can be
so, simply by starting with the mixture at idle/cut-off, rather than at
full rich.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"