If a quick cleaning with a thin wire doesn't work, I suggest you wait until the next time the water pump is serviced and the lower unit is dropped. There is a space in the LU casting where the pitot hole connects t. It is also where the spedo water flows. That space can get clogged with gunk or general buildup which can be hard to clear just using the pitot hole.
Also be aware that some motors route the water tube to a pressure sensor which sends an electrical signal to the gauge and some models actually run a water tube all the way to the gauge. I mention this since it is possible that the pressure sensor is acting up ( but not as common as a clog in the pitot tube.)
Some folks have used compressed air to blow into the water tube under the cowling to clear the pitot but there is risk that the hose will pop out of its fitting and in that case, the lower unit has to be dropped to reattach the hose.
Also be aware that some motors route the water tube to a pressure sensor which sends an electrical signal to the gauge and some models actually run a water tube all the way to the gauge. I mention this since it is possible that the pressure sensor is acting up ( but not as common as a clog in the pitot tube.)
Some folks have used compressed air to blow into the water tube under the cowling to clear the pitot but there is risk that the hose will pop out of its fitting and in that case, the lower unit has to be dropped to reattach the hose.
