I have twin 200 yamaha's (1993) I was cruising at normal speed today (approx 4000 RPM) and my port engine began to vibrate and dropped RPM's to approx 3000. I stopped and looked at the engine and not seeing anything I started running again. It ran fine for approx 5 minutes and then did the samething again. I stopped, turned engine off, tilted it up to see if I had anything on the props but did not see anything. I started the engine again and it ran fine the rest of the ride home (approx 10 minutes). I ran it hard for another 5 minutes to see if I could duplicate the condition. When I got home I started on the muffs and all was fine. What could have caused the vibration? It seems that it went into SLOW mode but I did not hear any alarms. Also, if it went into SLOW due to overheating I do not believe that it would have run fine without sitting for a few minutes to cool down. Any ideas?
