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2003 Johnson 90 runs great for 10-20 minutes

hunley5

New member
I have a 2003 Johnson 90 that has me pulling my hair out. I have had several Johnson engines in the past that has needed some work, but I am having trouble with this one.
As of now the engine starts and run fine (although a low idle) immediately jumps onto plane with plenty of power. The boat will run for anywhere between 10-15 minutes before feeling like a rug has been pulled out from under me. It completely looses power (at least 2 cylinders) and gains power back a few times before I throttle back. It will still idle, but does the same on and off power if I try and take back off. I can then fish for 30 minutes or so, and clears right back up and runs fine for about the same amount of time again.
I have replaced all fuel lines from the tank to the carbs, rebuilt all 4 carbs, replaced thermostats (then removed them completely). I have replaced both coils, all spark plugs, and all spark plug wires. I have removed the anti-siphon with no change. I have removed fuel lines and tried an alternate fuel tank.
I haven't tested my power pack (I don't seem to have the right equipment) nor have I tested overheat buzzer. The tell tail is spraying strong so I do not believe it is overheating.
Also, pumping the fuel bulb does not change anything when this happens.

The carbs have been off and back on 2 times with no changes. I am almost certain it is always going to be a power pack problem in my scenario, but I wanted some input before I drop that much money on something when I may be overlooking a simple problem.
 
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