I've a 1989 90hp Yamaha on my 17' aluminum skiff. The motor has always run fantastic, but recently it has started acting up a bit. If you run full throttle it the motor will bog down like it is flooding, but it never dies. If you pull it back and wait about 30 seconds it will take right off again. If you run it at about 3/4 throttle it doesn't do this. What could be causing this Problem? It also doesn't seem to matter if the engine cold or has been run all day.