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The FICHT engines are computer controlled. To properly diagnose the engine you need to have it diagnosed by a shop with the proper software. You could have a sensor that is not reading correctly and the computer is compensating causing hard starting.
The engines of that era are notorious for fouled spark plugs. But before just replacing the spark plugs note they are indexed to the proper direction in the cylinder. You need to make sure the new plugs are indexed as well. A mark on the plug with a marker will work.
You also need to check the fuel pump is putting out the proper fuel pressure. A fuel injection fuel pressure gauge can tell you what yours is doing. A engine slow to develop pressure will cause hard starting.
Do you know the fuel system is full? Fully primed?
Any signs of excessive fuel in the exhaust on the water?
Is this something that has been ongoing or just started? Has the boat been sitting?