Motor shakes at full throttle

I have a Mercury 125 that shakes fairly violently at full throttle. If I back it off just a bit, it runs smooth. I just had the lower unit replaced and the stainless prop reworked, and I never had this issue previously. Now, am I having cavitation problems (reworked prop a little different size now), spark plug issues, etc? I am really hoping I didnt blow a head gasket or something when my old lower unit went out and the motor revved up. Just curious if anyone has had a similar issue or may have some insight. Thanks.

Something is clearly out of balance

Prop

Prop shaft / take off

Spindle

It could be one of a few issues. First being the prop isnt quite right after they re worked it.
You may also be hitting your rev limiter at wot causing it to shake some while it drops cylinders.
Im not real up to speed on my mercury gear cases but they may have gotten a different gear ratio case than the original, if there is one.
It wouldnt be a head gasket issue since that motor doesnt have one. It is a blind bore cylinder head.

My first first step would be to bring it back to whoever put on the lower unit and have them check it over. I would also try running a different prop on it to see if that solves the issue. If a different prop doesnt solve it than it is the lower unit itself.

I’m praying it is a prop issue…of course those arent real cheap either. I dont think it is an RPM deal…on my old lower unit and prop I could hit the max (5250) but now I can get to about 5100 and thats it. I wonder if it isnt a gearing thing with the lower unit. I bought a new aftermarket one instead of going the rebuilt Mercury route…supposedly the gearing and everything is the same. The problem with taking it back to where I had it put on is that I’m the one that put it on. Thanks for the suggestions.

sounds like an out of balance prop or bent prop shaft

PROP

re: dealer installed wrong prop 13^ and it would hit the rev delimiter at full throtte, like hitting a big log, put on a 15^ and great

x2….on bent prop shaft or out of balance prop! try another prop! take it back to whoever rebuilt it! Good luck!

Well, tried a new prop and it does the same thing…runs like a top up to 90-95% throttle, then it starts shaking. I cant believe the prop shaft would be bent, its brand new…unless it got bent during shipping somehow.