I have a 03' 9hp Honda Go-Devil that I just bought today when I took it out it starts right up and runs great till I tilt it into the water. When the prop is about half way in it dies. I tried full throttle half throttle and no throttle and it still dies. I put fresh gas in it and checked the plug and it still dies. I did all these in my driveway with no water and the same thing , It still dies. Anyone Know what I need to do to fix this? ( It runs great when it horizontal it only dies when i tilt it)

Check your oil. Maybe your oil sensor kicking in.

I vote for the oil sensor shut-off doing it's job and not enough oil in the case. Second guess is an air leak in the fuel line someplace. Duckdon