2002 Nissan 50 TLDI over revs and slows down when trimmed up past center.

[lmbr]

Service tech said from cavitation but this started about a year ago and getting worse. When I lower the motor it stops. Recently installed a Humminbird hi def transducer. Previously had a standard compact ducer. Would that cause that? Before the compact ducer I had a DI ducer and don't remember having any problems. If that can be the problem, where should it go?

 

[stikboyy]

Its not from cavitation, its from ventilation. When you trim the motor up to high the anti-ventilation plate (the flat piece above the prop) will break its seal with the water and allow air into the prop causing it to blow out. Either your motor is mounted too high on the transom or you are just trimming it up to far. Your transducer should be mounting a minimum of 12" to the starboard side of the motor preferably. It could be introducing some small air bubbles into the prop but not enough to cause what you are describing.

 

[pvanv]

But it is true that the transducer could cause the electronics of the motor to get weird also.