I am having a problem with the boat I have. Its a '82 Avenger 17' w/ a 1968 mercury 1250. The problem I am having is that it feels as though the motor is spinning freely until and takes a longer than normal time to plane. I can give it 1/4 throttle and we start moving, 3/4 throttle it acts as though its cavitating. I am not sure the engine is in the right spot, the tilt (I don't have power tilt). Basically the engine is straight up and down, and not sure how far from the bottom of the boat the prop is. Any ideas?