Need to prop right for the motor to run at least middle of its wot rpm range although max wot rpm range is preferred. Will need to install an induction tach for that enterprise, go for a wot run as usually loaded and compare the max wot rpm achieved to the min-max wot rpm range factory stated and install a less prop pitch from current installed prop to pull wot revs higher...It's much cheaper than swapping 50 HP motor parts to a 40 HP motor.
Happy Boating
