try this: Explain what you mean when you say the motor cavitates. Some of us think it's the motor running poorly. You posted about shaft length, in context of some performance issues that are a little open ended.
Saying it had a certified mechanical review won't feed the bulldog, particularly when you go on to describe problems on a new-to-you motor. Would be looking for things like compression numbers, verified spark, maybe more on what you mean by rpm issues. Does the motor idle smoothly, for example, and run smoothly when you throttle up, or does it stumble? Any ignition work? l.u. oil full and clear, gas and oil fresh at the proper mix? Is the operating temperature good? Somebody do some water pump work recently? Other lower unit work? Anybody replace the prop on that motor, or maybe examine it to see if the hub was spun?
Why did it go into the shop in the first place (you or the PO brought it there because of some specific operating issues?) What's the history of the motor? It looks like there is some corrosion at the lower unit -- maybe used on a pontoon, maybe rarely. Fresh water motor?
not interested in pushing your buttons -- but do you work on outboards? Done some testing on this one before purchase, or know of work done?
Shaft lengths and jack plates aside, could use some convincing that the motor is in good mechanical condition -- some better hints about the operating condition of the motor.
Here are the photos asked for.
