I am a marine tech and I rig new pontoons on a daily basis and your problem is any one of these 3 things and can be all 3 . Wrong prop, engine is mounted in the wrong holes( typically Yamaha is mounted in second hole down) or incorrect shaft length for the boat. Which can be fixed by adding a jack plate. If the boat is new take it back to the dealer. Pm me if you have any questions. Hole this helps