Loss of power

[rcs1ab]

I have been working on a 88 70 hp Evinrude. I have resolved my overheating problem by replacing the head gasket and cleaning out the salt build up around the cylinders. I check the compression of the cylinders and it seems to be fine. 127-130 on all 3. I have rebuilt the water pump and fuel pump. I replaced the plugs and took the boat out this weekend. She ran great for 5 minutes and then slowed down. At full throttle she would not accelerate. She ran, enough to get me back to launch and started up fine to load her on the trailer. When I had the head off I noticed the number two piston was alot dirtier than the other two. Could the coil or power pack portion of the number two cylinder be breaking down as the engine heats up.
Thanks

[boats.net]

Could be ignition breaking down on one or more cylinders(check with a timing light0, could be a fuel restriction(vacumn and pressure test fuel system), fuel pump problem or dirty carbs.