Larry Kraus wrote:
Did you try switching the manifold pressure hoses between the left and right indicators to be absolutely certain that it's not an indication problem? One other thing might be to try disconnecting the manifold pressure line at the gauge and blowing back toward the crankcase with low pressure shop air. That cleared up a similar problem in a DC-7 once. The line had a small amount of oil or carbon restricting it slightly and blowing back cleared it.
I might try that. But, if it is the a gauge or gauge line issue, wouldn't I have uneven fuel burn or props out of sync when the needles are matched on the gauge?