That picture of the clamp really helped. There are two installed on the throttle cable, one more on the shifter. I would not have known what they were.

There were two issues, one is that there is an internal return spring in the Yanmar throttle assembly that would be better suited for a bear trap. The second I would have never picked up on without operating the throttle assembly. The angle at which the throttle cable was clamped to the engine itself did not allow the cable to operate smoothly within the arc of the Yanmar throttle lever. As the throttle advanced the metal tip of the cable sheath was bent down. The further you advanced the throttle, the greater the bend. When you released hand pressure on the throttle lever at the wheel, the cable sheath would return to the straight position, acting exactly like another spring.

The fix was to loosen the clamp on the cable at the engine and adjust the angle to more of a straight shot. That allowed a smooth movement of the cable end without bending. The second was to move one of the tension clamps nat described closer to the end of the sheath and adjust to a proper tension. The throttle will not stay at WOT which is fine by me, but will remain at any other setting without creeping back to idle.