1991 mercury 200hp 2 stroke

by Seàn
(Ireland )

1991 mercury 200 hp 2 stroke

The engine runs perfect on the mufflers but when I put it in the water it’s flat/dead. It will only Rev up to 1800rpm but will hold constant at 1800 and will drive up and down the bay as often as I like but will not rev up anymore. Fuel lines and filters are replaced. Carbs look spotless. I replaced the stator but still the same problem. Incidentally if I put the boat in reverse in the water it will rev up to 4500rpm no problem?? Anyone got any ideas please?