My engines were running fine all day, trolling and all. Went to bring engines up to speed for the ride home and my port engine won't sync up to my starboard engine. They were perfect on the way out in the morning. I turned both engines off, restarted, and both engines synched up perfect, then 5 min later, same problem with port engine, speed just went down to 2400 rpm's while starboard was at 3200. Any ideas?