2003 yamaha 50hp 4 stroke, want start, was running at idle and high rpm

[032052]

I just purchased a 2003 yamaha 50hp 4 stroke pontoon from ins company, gas tank was empty and looked as if removed and drained for hauling. Started and ran at idle and high rpm, mid range wanted to cut off, now only starts with starting fluid and at high rpm. Changed plugs, pulled carb drain screws, pumped primer gas flowed, just went and removed gas cap, started with ether and ran much better but just at high rpm.
PLEASE HELP
THX Mark