Thought it was a spun prop. Bought new prop and still doing same thing. Start fine and boat accelerates thru half throttle and into full throttle. Then all of a sudden forward motion stops engine rpms go up. I have to back off throttle until it feels like it catches again.. just bought 13 3/4 x 13 porp. This motor is on a 27 foot pontoon. Is this just to much weight for this prop to push?