While returning from a sail yesterday I lowered the motor (it tilts up out of the water) and fired it up to enter the river to my mooring. As I happily (or unhappily - hate the motor) chugged along all of a sudden I was shocked and pannicked to see barely any water streaming from the water pump pressure check tube. I lowered the RPM and continued as it is a very buisy channel and kept my fingers crossed. Back at the mooring I tilited the motor up and checked all of the intake ports, the streaming tube and the cylinder temp. All seemed normal. Since it was cocktail time I was going to leave it for another day so it sat out of the water for a half an hour. Well it finally got to me and I had to check it further. I lowered it back into the water and fired it up. The water pressure was now fine. High and low RPM. I let it run for a few and it kept working. Is there such a thing as vapor lock or a priming prolem with OB's? Has any one heard of an impeller being loose on the shaft so it is intermittant? Could deposits be nearly clogging the system? The water out there is pretty free of dabris and I saw no sign of blockage.