25 hp Johnson vibrates at middle speeds

[bbushay]

I have a 25 hp Johnson outboard 89 on a 14' pontoon. Runs good at low speeds and at full throttle but in between it there is quite a bit of side to side vibration. I do not have a history with this outboard. I got it to replace a smaller outboard. Visually the prop looks good does not seem to be bent or have any dings in it. . I am looking for ideas of what I should be looking at and any diagnostic tips

 

[jakedaawg]

Compression test.

Open air gap spark test set to 7/16" with throttle advanced part way.

Fuel sample into clear jar.

Some of these do shake a bit though, it sometimes get worse with worn out linkage and such.