i have a 1994 starcraft 2010 with a 5.7 liter mercruiser I/o. the motor revs up past 2000 rpm with muffs or in neutral in the water, put it in gear and it wont get past 2000 rpms. I have changed fuel filter/water separator, plugs and plug wires, pickup coil, rotor and distributor cap, ignition coil and fuel pump. carb seems to be working ok. it is a 4 barrel, not sure what brand. any help would be appreciated.