Re: i'm a newb - just joined
Assuming that the engine is the right shaft length for the boat...... the cavitation plate just above the propeller whould be approximately 3/4" beneath the bottom of the boat at the transom, the following would pertain.
If the engine pushes the boat fairly normally at a low rpm BUT has the boat slow down and the rpms increase at the higher speed, that usually indicates that the hub within the propeller is slipping and requires rehubbing at any reliable propeller repair shop.
What is the model number of that engine? Usually numbrs on a small plate attached to the port (left) transom bracket.