runs with fuel off

Thanks in advance for any replies, I'm new here. I have a 88 seadoo bombardier which was given to me 3 yrs ago from original owner. It sat for 4 yrs before I got it. It started and ran great for yr 1 & 2. Yr 3 a friend took it up north and ran it with no plug, it flooded, not sank, he said...