Engine Trouble... anyone got any ideas??

[CaptScottNC]

Engine troubles of course on the maiden voyage. Let me give you some background and you can tell me what you think if you don't mind.

1995 Mercury 3.0L Black Max 225hp with brand new powerhead and lower unit. Boat was test drove in Florida about in April and then I've had a hard time getting it up here. Compression is perfect and the boat ran 46mph on the sea trial done by the surveyor. No problems.

I took it out for the first trip and we idled out... boat did fine.. smooth idle. Got out of the No Wake Zone and smoothly pushed the throttled down. She started to come out of the hole and on plane and at about 15 mph she completely lost power but did not quite shut off. This was about 2 to 4 seconds after putting the throttle down. It coughed a little and I backed the throttle off and then she went right back to idling smooth. I tried it again and it lost power much quicker this time never trying to get out of the hole. The bulb felt flat and my first thought was a fuel restriction of some kind. If I pumped the bulb up hard it would try to get out of the hole and die back. Well it ran just fine at 1200 rpms but if I eased up over that much it would lose power and almost shut down. Sometimes it did shut down. Ok.. now we decided to just troll for blues about 5mph or 1100 rpms. Boat did fine but if we rocked hard by a boat wake it would cough and sputter and die or possibly not die and get back to idling once the wakes passed. It seemed to need to rock pretty good to make this happen. Normal boat wakes didn't do it but a big sport fish or good swell would cause the engine to struggle and cough even at 1000rpms. So now I'm wondering could it have something to do with floats in the carbs or fuel sloshing around in the gas tank or what? It does it very soon after the boat rocks hard.

Ok.. put it on the trailer I looked at the water sep filter and it was rusted onto the aluminum housing and the housing was completely corroded. No hope of even saving the frame of the sep filter. I bought a new Racor filter and frame and installed it along with a new section of line from the filter to the engine. New bulb and all. Bulb pumps firm very easily. Thought a check valve could be messed up in the bulb and it was a bit old. Ok... took the boat out today. Idled around fine and the boat even ran fine out of gear on a hose up to 5000 rpms. Idled around smoothly about 1200-1300 rpms casting at spanish then decided to head out to the inlet. She came up on plane almost probably reaching almost 20mph and I thought it was fixed then it suddenly died again. Then the same exact problems. Only thing that was different was that it started idling much rougher after that and then might idle smooth for a while. Rough for the next 20 minutes and then smooth for a minute or two but if you pushed the throttle much you got no response and it would lose power or shut off.

The tank is half full and sat half full often I would imagine down there in florida. Could it be water in the fuel tank?? Do I have a water sep filter in this model engine as well? Honestly I have to look agaain to see. The sloshing is making me wonder floats, carbs, water? The boat sat too long with some bad fuel and then something about trailering it 12 hours sloshing around a half empty tank?? any ideas???