Just stumbled on this, pretty positive the line I purchased is 3/8. I just found 5/16 new line and bulb and the female connector that states it is for pre 1998 mercury engines, maybe this second round will be the trick. Only thing I really changed... Baffling how this small of an error could cause the boat to bogg down trying to plane.
''Taking into account the length of the fuel line, when trying to increase or maximize fuel flow, it might seem logical to use larger-diameter fuel line, however this may not always be true. The fuel pump on the motor is working to lift the weight of all the fuel in the line from the tank, so if you were to go from a 5/16-inch line to 3/8-inch line, you will increase the volume and the weight of the fuel in the system, and this could make the fuel pump work harder, mechanically restricting fuel flow as opposed to / by volume''