i have a 25 hp yamaha outboard motor, 2 months a go a friend and i went to the river and it ran perfectly.I went back to the river two or three weeks ago and it ran good for 5 minutes or so and then cut off. When choked it crank easily, ran for another 5 minutes or so and cut off again. This cycle continued until i loaded it back up, 45 minutes or so later. Any suggestions on what i could try? thanks