Mariner 40 Mag won't run

[DGREIN]

I'm having a issue with my 91' Mariner 40 Magnum .1st time out this spring it started fine and ran smoothly while I motored at 1/2 throttle through the shallows. Once out of the No Wake area the I speeded up to to cruising speed toward my destination about a mile away. After a coule hundred yards the engine slowed to about 6 mph and thats all I could get even a full throttle. I continued to my spot and used the trolling motor to fish the area and when I finished the motor won't start. Used trolling motorto get back to the landing. At I put the motor in a barrel of water and it started right away , ran fine . I did notice a water leak from the back corner of the exhaust cover gasket. Thinking that water was leaking into the cylinders I replaced the exhast cover and baffle gasket. Now I can't get the motor to start. I checked the spark is good and the compression is alright. My next guess would be a fuel issue. Any idea where to start?