"Tony" wrote

wing tanks or header tank? has there been any consistency in fuel
level during these events? ive had engine problems in airplanes with
header tanks at extreme nose up attitudes and low fuel levels. your
"negative G" towpilot could be on to something. is there an engine
driven fuel pump on the pawnee, even with a header tank? have you
checked to make sure it is working?

ive had a valve stick (on a cessna 150) and it was VERY noticeable,
not "very slight" roughness.

*********************

It has a header tank but the problem occurs regardless of fuel level. If
anything, it is almost always full or at least half full when the problem
occurs.

I think part of the reason that the roughness isn't as bad on the 0-540 is
because you're losing 1 out of 6 instead of 1 out of 4 when a valve sticks.

Bruce