1989 Ford 2.3l bogging

Please Help, Im at wits end.
I have a 1989 Four Winns with the Ford 2.3 l and OMC Cobra outdrive.
My problem started with the boat 'hiccuping' at cruising speed.
Initially evry 15 minuts and eventually every few seconds. In an attempt
to fix this problem the boat now will not generate enough power to plane.
It wont turn over 2500 rpm under load.

Here is what i have done so far:
change plugs, plug wires, distributer cap, rotor and points
checked and rechecked the dwell and timing - set them to factory specs
removed distributer and verified that the weights and springs appear to be functioning
changed the coil (replaced with one from the auto parts store and then I broke the original so i cant put it back on :-(

replaced the fuel/water seperator, rebuilt the carbureator, changed the fuel filter going into carb
ran a check on fuel pump for both pressure and volume - checks out ok
ran the boat from an external tank (no anti-siphon valve)

I have also checked that the ESA valve apears to be functioning correctly.

All i have succedded in doing is slowing the boat so it wont even plane anymore.
Help PLEASE!

check the plugs for oil i had a leaky head gasket and mine did the same thing

When was the last time the timing belt was changed. I beat my head against a wall for about 4 months trying to figure out a power and performance problem with a 2.3 liter ford engine did all the same things that you did to the boat and finally found that the belt had stretched enough to allow the valve timing to be off enough to hinder the power of the motor. The belt did not jump a tooth it just stretched. A new timing belt brought the power of the engine back up to proper performance.

Thanks for the feedback. I finally have given up and brought the boat to a professional.
I hope to have an answer soon.