I have a 1989 yahama pro v 150. When the boat is on plane the steering becomes very hard to turn in either direction, it is fine at very low speeds. Any help would be greatly appreciated.
I have the same problem as you, albeit on a smaller scale, 18' pontoon with a 50 hp Mercury. same deal though, on trailer i can one hand it, but put a load to the motor and it is a two hand job. If you find and answer i would appreciate any help, i will do the same should I by some miracle figure it out.
I doubt it is anything with the steering shaft, tilt tube, or old grease. Does it have cable or hydraulic steering? I have found that with cable steering, due to the motor's inclination to keep itself straight, it can be stiff keeping it in a turn.