60 Mariner slows to idle while cruising

[joed]

1995 60 HP mariner 3 cylinder 4 stroke.

The issue. While cruising to my fishing spot at about 3800-4000 RPM, 18 MPH the engine will suddenly start slowing as if I pulled the throttle back. I jam it forward full throttle and takes off. I can keep it running fairly well by working the throttle up down constantly. Water is peeing out fine. No alarms for oil or overheating.

What I have tried.
Suspected fuel issue so I switched over to my 5 gallon kicker motor tank. Same issue.
Inspected all the throttle linkages and do not see any issues.
Spark wires all look intact. No broken plugs.
No signs of fuel leaking inside cowl area.

Next thing I will do is check/change the fuel filter. Looking for any other ideas.

 

[joed]

Pulled the plugs.
Two of them, top and bottom are black and carbon looking.
Middle one is clean and tan coloured.

 

[joed]

I guess I stumped everyone. When I do find the problem I will post the fix.

 

[jerseydevil]

I had a similar problem last year w/50hp Merc. I couldn't go past 1/2 throttle w/o boggin down. Wound up rebuilding all 3 carbs & problem was solved. Ethanol is really screwing things up royally. And I use Star Tron etc. Good Luck

 

[joed]

Boat is up on trailer for the season now. I may just take it in to the dealer. I have not decided yet.

 

[joed]

Did a compression test. All three cylinders are 110-115.