I have an older mariner 25 hp ( pre mercury) serial # 695s-015335. The motor will start like normal. after ten minutes or so, the motor wants to bog down and lose power. I have put muffs on the motor to try and find something out but have had no luck. I can tell you that the pisser water is cold, and that when the spark plugs start to warm the engine starts to fail. After 30 minutes or so of sitting the motor will fire right back up. I was told that it could possibly be the coil. that when it gets warm it shuts the spark down and that is the reason for the plugs having fuel on them when they are pulled.
