Outboard issue ?
 

I've been having an issue with my Johnson 90HP two-stroke.

Motor idles fine.
No hesitation going from wake speed, to full throttle, really quick !
Issue only relates to moving at wake-speed, at which point the engine seems to vibrate. Once I go past 'wake-speed', the engine smooths out and runs fine!

Other than this issue, this has been a great engine !

Thoughts about this issue ?

If you have a stainless steel prop, it may be a bit loose on the shaft and that would absolutely cause this issue. See if prop can slide fore and aft or rotate a bit on the prop shaft.