For the last couple of years my '87 351 has started and run flawlessly. Last week I puttered at about 400 rpm for about 4hrs while my son did a 9 mile endurance swim. Each time I stopped the motor to feed him, the boat was harder to start, other than that the boat ran perfectly. Toward the end I was glad I had a new battery. There was a "sweet" smell after the hard starts. I change the plugs and fuel filter every year. Anyone else with this problem, or insight into the cause?