1991 48 hp SPL runs great until warmed up, then shuts down to idle.

I recently bought a 1991 Johnson 48 hp SPL, model J48ESLEIM. The seller informed me of a "bogging" issue after it warmed up, but I figured for the price, it was worth it for the learning experience. The boat cranks up and runs great for the first 10 minutes or so at WOT, then the motor loses all power as if its been throttled down to idle speed. It does not stall out. It continues to run and once the the throttle/shifter is brought back to neutral, it will run fine at around 1/4 throttle. If I shut it off for a short period of time, it will plane out again, but still lose power when it warms up. The warning horn gives a chirp when the key switch is activated, but no warning horn when motor loses power. It maintains a good telltale stream.

I've replaced the ignition coil, rebuilt the fuel pump, replaced all fuel lines(boat side and motor side), rebuilt the carbs and checked float settings, changed spark plugs, and replaced one of the spark plug wires(found a bad spot in it). Yesterday, I pulled the flywheel and checked resistance readings on the stator assembly. All readings were within limits, per the service manual. Not sure if it could be related, but I did change the gearcase oil in the lower unit, and it did appear to have some water in it. I'm not sure when it was last serviced. I've also got a new water impeller and plan on installing it this weekend, since I don't know the age of the current water pump.

Spark and compression seem to be fine when the motor is not under a load or at WOT.

I'm leaning toward the problem being the power pack. It seems to be original by the part number on the ignition module.

Here is a video from Monday of the problem. Is this S.L.OW mode activating?
http://youtu.be/f95tvwHS7g0
first 2 minutes of the video were edited out of the boat running fine to show the problem.

Update....I've installed a new impeller in the water pump. The old one seemed to be in rough shape and small chunks of plastic had made it up into the thermostat. I tested the thermostat and it works fine. The temp sensor is functioning correctly. I thought there might be a possibility of overheating causing the slow down, but I wasn't getting a warning horn. I tested the warning horn and it seems to be working.

I've found a leak at the fuel pump. The screw that holds the filter to the pump snugs up, but loses grip when the fuel bulb is pumped to firm. Unfortunately, the part of the fuel pump, where the screw tightens, is plastic. With the fuel filter off, the screw will snug tight, without any chance of coming loose. The thickness of the fuel filter is causing the screw to lose threads to grip. I might try a slightly longer screw to temporarily relieve this problem. I will probably need to get a new fuel pump, even though all the other parts are in good shape.

Another update...compression on both cylinders is right at 120. Spark test jumped 3/16 gap.

Good spark will jump a gap of 7/16" or more, does it do that ?

Yes, it does jump 7/16, not 3/16. I took it out on the lake today and brought a timing light. The motor ran great for 3 or 4 miles and timing was right on the mark. Once the motor warmed up, it bogged down like in the video. We checked the timing again and it was almost 180 degrees off the mark. Once the motor had a chance to cool for a short time, the timing was back to around 19 degrees.

Here's a follow up, in case anyone else runs into this problem. I changed out the power pack with the CDI conversion kit from CDI. The conversion kit moves the ignition module out from under the flywheel. The boat is running great now.

after watching the video...it is definetly loosing spark...power pack?