Merc 90 hp 4 stroke mystery vibration

[skijunk]

2015 Mercury 90hp 4 stroke. A few weeks ago we were riding at about 1/4 throttle and all of a sudden the engine speed winged up as if we had hit something and began cavitation. I turned it off, raised the engine to look at prop. I couldn’t see anything but thought maybe we hit an Asian carp and tweaked the prop. I couldn’t tell there was any damage but I wanted to get a stainless one anyway.
We haven’t used the boat since.
Today I installed my new mercury Stainless inertia prop. I am getting the same vibrations.
The engine is a smooth as silk at idle but when I engage forward or reverse I get the vibration.

What has happened ?

 

[Swagonmaster]

You might try looking at the end of the prop shaft with it running with the muffs and in gear to see if something other than the prop might have gotten bent, if nothing there try pulling spark plug wires one at a time to see if there is a dead or weak cylinder. That is much less likely but obviously something has changed.

 

[QBhoy]

Is the prop hitting the trim anode ? Is it a ct model ?

 

[QBhoy]

Check if the white exhaust seal ring is loose behind the prop. Getting to be a common issue on these new mercs.