rough running C-182

"R&A Kyle" wrote in message news:1HCkd.12833$z_4.9667@trnddc07...
Can anyone suggest a cause for a slight roughness in a well maintained O-470
(1958 C-182). The mechanic has checked both mags and harness wires and
plugs, installed a rebuild carb and balanced the prop (which required very
little correction). In flight checks of carb heat, mags and unlocking the
primer pump all show no effect. Roughness appears above 20" MP at any RPM.
Engine mount checks ok.

Any suggestions would be welcome.
R Kyle


Plugs are worth checking again. We've had lots of trouble with
Champs in the past, and went to Auburn/Unison plugs years ago because
they were so much better. Now we're finding the Unisons arcing in the
shield barrel when the pressure reaches 120 or so, and the spark
weakens sooner and causes roughness at climb or cruise settings. A
month ago I installed a full new set in one of our airplanes and the
roughness cleared up immediately.

Dan