I have a 25HP 1990 Johnson Outboard motor with an electric starter that has worked well for many years until now. It will cold crank and start just like it always has, but after 5 to 10 minutes of running wide open it will begin to sputter until it shuts down with a rather violent jerk. At this time it will not restart. I have found that if I tilt the motor up and out of the water and let it sit for 5 to 10 minutes, I can lower it and start it. It will again run for 5 to 10 minutes and shut down. When the motor is lifted, I have noticed a small amount of un-burnt oil dripping from within the carborator intake of this 2-cycle engine. It seems like the engine is flooding only after running wide open for 5 or so minutes. This engine has always had trouble idling. What's going on?