Fuel was definitely old. Due to a knee replacement we only used the boat once last year. So the gas sat for at least 7+ months. The first trip this year it ran really rough, I assumed due to moisture in the water from ethanol. You may be on to something, because this trip we were down to the last of that tank so maybe that is a contributor to the issue. I did put a can of sea foam in it after the first trip where it ran so rough. The second trip it ran better, but still missed now and then. The 3rd and 4th trips (this latest being the 4th) it ran normal right up until it overheated.