At 1115 Pacific time, a Bellanca 14-19 lost engine power when making a missed approach at the Napa County Airport and was ditched in San Pablo Bay. The pilot was not injured. The flight departed the Camarillo, Calif., at 0730 that morning and had diverted to Angwin during a period when Napa was below approach minimums. The flight departed Angwin at 1020 on an instrument clearance to Napa. The pilot said he departed Camarillo with full tanks, which gave him four hours of flight time plus a 45-minute reserve. The pilot said he made his approach too high and the tower controller instructed him to execute a missed approach. During the climb out the engine started to sag and the airplane would not maintain altitude.