If your motor has the square fuel pump, and I think it does, this could be The one of the very few confirmed ethanol problems. Ref: Mercury Service Advisory No. 2001-17. The symptoms are as follows: you are cruising along at WOT all of a sudden it is like someone turned the motor off. The motor will start right back up but will continue to do this unless you throttle way back. The problem is caused by the check valves in the fuel pump and the fix is to rebuild the fuel pump. You must get the Mercury kit as it contains new style check valves. What happens is over time ethanol causes the edges of the check valves to curl up slightly and they no longer seal properly. The newly styled check valves do not have any rubber on them and are just round pieces of plastic type material.
Fair Winds and Following Seas
Bill H. PTC USN Ret
Chesapeake, Va