Hi all - looking for a place to start with this one. We have a 1982 3396 Carver Mariner with twin 350 crusader engines. As we were coming back from a day trip all of a sudden the engine sync gauge would drift to the port side ( about 3/4 of the way ) then after a second or 2 it would come back to center. You could hear a difference in the engines so it shouldn't be just a gauge issue. This would happen every 10 or 15 minutes - The Tach's did not show a difference in RPM in either engine but given the sync was only off by a little I am not surprised. We were cruising around 7 / 7.5 knots. Any thoughts would be appreciated. As an addendum - We went out again and it the issue did not reoccur until we we out about 40 minutes or so.

Thanks in advance