So I have a 1989 Nissan 90hp on a 16 foot Nissan boat and it is having some problems. First time off the landing I can get it to plane no problem but only stays up for a minute or two and once the motor is warm it won't come close to getting up. It's like it revs up fine to about half throttle and then any further then that you can hear it just bog down and have no power. I have checked the things I know how but by no means am I a mechanic. Compression is 132, 131, 131 in cylinders top to bottom. Spark is strong and fuel lines are not obstructed and tank is venting fine. Carbs are also clean. Beyond that I don't really know where to look. Any input is appreciated!!