I have a '91 150hp XR-4 mercury outboard. Originally it had a small gear case and it maintained 15 psi of water pressure at 5500 rpms. The gear case broke and was replaced by a large gear case. Since then the water pressure is only maintained at 7psi at 5500 rpm. The system has been flushed out and water pump impeller replaced several times. The engine doesn't seem to be running hot. There is pretty strong water coming from the tell tell. The water pressure at idle with both gear cases is about 2 psi. I have been told the engine should maintain 15 to 17 lbs of pressure at 5500 rpm. What could have caused the reduced pressure?
