check engine 1999 225 evinrude

I have a 1999 225 evinrude motor that after running full speed for 7-10 minutes the check engine buzzer goes off. Mechanic hooked up to computer the code was water in gas. He checked gas with some type of gadget that detects water % and replaced filter, I checked the gas by empting some in a glass jar and let it sit - nothing. The last time this happned I unhooked the censor and the buzzer still went off.

The engine starts to spit and sputter some and eventually shuts down at slow speed. After sitting for 4-5 minutes it will restart like nothing is wrong.

2 years ago I replaced the computer board/head ($1800) - not sure of name. I was told this part often needs replaced in this motor. Could this be the problem.

Any help would be greatly appreciated.