1988 force 125 no power at wot

[rcav8ter]

I need some help guys. I went out Saturday morning (St. Lucie inlet) motor ran fine, at noon It decided to cough or hesitate then I lost power. At wot I had 2000 rpm and cruising at 7 mph of course Im 6.5 miles offshore(ha ha). I stopped the boat pulled the plugs, changed them and no difference, so I began a long slow journey back to the inlet as I was heading back it seemed to gain more rpm and more speed by the time I was back in the river I was at 17 mph and about 2500 rpm. What could be the problem?
After I parked the boat cleaned it and flushed the motor, it idles fine and revs up in neutral without any hesitation, after I flushed for 10 min I checked the compression on all cylinders over 120 on all. Could it be the 89 octane e-10 gas? could it be Hess gas? I bought some Startron fuel treatment and put some of that in my fuel tank. Am I looking in the right direction? should I look somewhere else? Thanks, Chuck

[john from md]

Do you have an inboard tank? If so, put an canister type fuel filter in the line and use a water separating filter canister so you can see if you are getting water. Also, make sure mud dabbers haven't made a nest in your tank vent.

John