My SJ don't take rpm max sometimes (and nobody knows why...)

[optimizaide]

Could it be that you are experiencing water loaded up in the water box and pipe?
The same thing happens when you flush a ski on the stand at low rpm.
Once you are done flushing and try to rev up the engine to clear out the water, it just bogs and is slow to rev but as you keep it up and the water clears, the throttle response gets crisp again until soon it is firing off nice and sharp again.

i don't have the things to reduce the water coming inside the waterbox, so if i understand well, for you it may be that to much wtaer goes inside the wtaerbox and thhen on the pipe, and maje it hard tio rev?
I will also put the reducer on the wtaerline just to be sure ( i did not put it cause i don't like to make a lot of noise)

 

[OCD Solutions]

You can test this theory by simply revving the motor out of the water. Mine clears up after a few 4-5 second pulls on the throttle.
Just be careful to not do it too long and overheat the engine.

 

[wydopen]

This is what mine was doing in the thread I posted. Runs fine in the water breaks up out of the water when I go to clear out waterbox..once it sits for a day or so it rev’s fine