I ran my 1997 Johnson 30 hp in the lake last weekend for the first time in about 2+ years. It has been previously run in a barrel at home occasionally but only idling. It started fine at the lake and ran strong for about a minute. Then the rpms dropped and it would only run at idle speed. Initially I thought it was the fuel line. It had been kinked a little during storage. Changed it out and it did the same thing, ran good for a minute then powered itself down. I think there is a safety shutoff that limits the rpms if the motor starts to overheat. I was getting flow out of the pee hole and the motor didn't seem to be hot. I am going to go ahead and change the impeller as it hasn't been changed since I bought the motor 3-4 years ago. Maybe a stuck thermostat? Anyone have any ideas what the problem might be. Thanks.