Weak Johnson 150


I have a 1990 Johnson 150 on a 2100 pound Crestliner. Rebuilt the carbs, new plugs, fuel filters, compression even 90 all 6 cylinders, all cyl firing. Idles smooth, and starts to accelerate, but then levels off around 3500 rpm and tops out at 15mph. Just pushing water from there. Haven't touched ignition or timing, didn't understand what the book explains. Need some ideas on what to do next, or how to check timing components. Thank you!


Sounds like it is severely “over propped”. Have the motor tested on a test wheel. This will verify the engine is ok. Most dealers have these, older dealers anyway.  




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Mark C.


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