boat starts to “porpoise” to soon

I have a Bass Tracker Tournament V-17 with a 70 Horse Merc. on the back (power trim and tilt). The boat runs well and “jumps” out of the water, but I am only getting about 35 MPH out of it when the trim is set properly. As I begin to trim up a little more, the engine speed and boat speed begin to increase, but the boat starts to Porpoise. The motor does have a “Dolfin” on it. It has been suggested that the motor may sit too far in the water. Any ideas??

I’ll try to help you with the experience I had.First off,is your prop in good shape? I had a rebuilt prop on my motor when I bought it,and although it wasn’t all nicked up it caused a great deal of problem as it was rebuilt with the wrong pitch. Also I had raised the motor up on the transom so the center of the lower unit (prop shaft line) was equal to the base of the keel. That and the prop made the biggest difference. I added the whale tail and that took the rest of the porpoise out but cost me speed and ease of steering so I removed it. The trick now is to keep the motor trimmed down a little until I reach speed then trim it up and I’m fine. Hope this helps!