Your 40 HP Yamaha outboard motor is not shooting out water only dripping what is the problem?

Like most outboard motors, the Yamaha is water cooled. It takes water in from the bottom of the prop housing and circulates it through the system to cool the engine and lower transmission. The pump that provides the power to do this has an impeller (usually made of neoprene).

More than likely, the impeller needs to be changed. Also, if this has been an ongoing problem, there is no telling what other heat related problems will need to be addressed.