once the cavitation plate is above the bottom of the hull, the motor must be trimmed perfectly, or it's going to "porpoise" (bounce)
the solution is to lower the motor more, and/or add weight to the front of the boat
if you're driving into the wind, it's going to porpoise more than if you're driving with the wind
you may need to adjust the trim of the motor, if your motor has power tilt/trim, just keep fooling w/ the trim up/down until it settles. if your motor doesn't have power tilt/trim, you'll need to adjust the pin on the transom bracket so that the motor is closer to the transom when the motor is all the way down
weights, moving the battery, moving the gas tank, putting a passenger up there, are all ways people add weight to the front of the boat to keep it from bouncing
a 40hp motor on a 14' hull though, you've already got more weight on the back than what is probably recommended by the manufacturer of the hull, so there's only so much you can do with trim, you need more bow weight