Okay. I hope someone has the answer for me. I have a 15 hp 1997 evinrude 4 stroke it's a electric start. When I put it on the water it cranks up. It is on a 17 ft flats skiff thin wall fiberglass hull. when I open it up it will not get on plane maybe 10 mph max. then the primer ball will go soft. So I replaced the primer ball 3 times. after the I get to my fishing spot and then crank it up again to come back to the ramp it will go maybe 5 mph max. then it will sut off. I would start it back up after a few attempts and it will run 2 mins then it will shut pff again. Then a knocking sound will start while running. Then it will run all the way to the ramp but very slow. I have to keep priming the ball so the motor doesn't shut off because lack of fuel. But even then after running the motor trying to get back to the ramp that doesn't always work. The motor has excellent compression. The primer ball is good. Has new plugs. I don't know what the knocking sound is. Could it be a bad fuel pump? Under the Flywheel is a exhaust looking thing with a hose going to it. It releases smoke evey now and again . Well a few times when I trying to crank it up brief flames would come out of there. Please if anyone has any info please help me out