I have a 1997 40 hrs outboard it runs great at the start we can run for about 10 minutes great all out power, then it starts slow down and sputter till it shuts off. It will start back up and go for a second and sputter and die. If we let it cool it will run for a while and do the same thing. Any thoughts we have cleaned the fuel lines and replaced the line from the tank to the motor and the ball and cleaned the gas tank. Help please!