The last time I took my boat out last year my motor was not running like usual. Instead of running at 5200 rpm it would only go to 4700 rpm. I winterized, put in new plugs, new water/fuel separator and filter. I took it out this year for the first time, it was running nice for about the first mile, then the motor bogged down and dropped in rpms, almost like a cylinder isn't firing, then it would rev up and bog back down. I thought it was water in the fuel, so I emptied all the fuel, put in new fuel. I took it out today; for about the first mile it was running fine, then it bogged down and at 3/4 throttle, it was only going about 15 miles per hour, like it wasn't running on all cylinders. Yet, every once in a while it would rev up like the cylinder was firing again and then bog back down and drop in speed. At one point it seemed to be running fine again for about 5 minutes and then the problem happened again, and I took it back to port at 15 mph at 3/4 throttle. Any answers? My friend seems to think maybe one of the coils are going, but I'm not sure. It revs up, then down, up, down...???? The motor is a 1999 Yamaha 150hp Saltwater Series II. Motor is an Oil injected carbuerated version. I pump up the fuel ball, have 3 Carbs, oil injected. It seems they made 3 different models that year. One of my friends thinks it may have to do with the piston rings since the problem seems to happen after the engine has warmed a bit. I was driving back to port and it was running very slow, low rpms, 3/4 throttle, and all of a sudden it would "kick in", you could hear the motor rev up, sound normal, and the speed and rpms would rise, but only for about 20 seconds, then it would bog back down. ????