Fuel draw problem

My 26 Fortier, Bluejacket II, is experiencing a fuel draw problem. Since new in 2000, I have always drawn off both tanks and by keeping the port return slightly closed, the fuel burn was even. Starting last fall, the draw changed drastically. On my run to Freeport from Montauk, I burned 57 gallons with 47 coming out of the port tank and 10 out of starboard. This spring I ran the boat for an hour off the starboard tank only to verify that there was no fuel line blockage. All was normal at the full rpm range. For the trip back to Montauk just this past weekend I opened both returns fully, and burned 40 gallons, with all of it coming from the port tank. (see separate posting in response to JB Cape on the fuel burn difference). When fueling, the starboard tank backed up through the fill hole before anything came out of the vent. But when I removed the fuel nozzle, a few oz. gushed out of the vent. Anyone have any suggestions of how to fix this problem.

Fortier Boats Inc.  •  34 Riverside Ave.  •  Somerset, MA 02725-2869  •  508-673-5253