I have a fountain 10 meter with 7.4 liter mercrusair engine driving trs drives thru borg-warner transmissions. The starboard engine and periodically the port engine will over-rev and loose thrust when I am returning home after a day on the water. It never occurs on the way out. But on the last two return trips, approx 3 hours later, I have had the problem. When i lower the engine speed, it seems to catch. Came home tonight only developing 12 mph, normally 50-70 mpoh. Any suggestions. Thanks in advance WB.

Transmissions going out?

Sounds like your trany is slipping. Pull them both out and freshen them up.

before I pulled out the trannys and rebuilt them, I would look at and smell the oil if it is brown and smells burnt, then pull them. good luck.