Hey all, I have a 1985 Yanmar 1GM10. At low RPM (e.g. 1600), the sea water flow out of the exhaust looks great. But when I'm up near 2800, the flow stops almost entirely. I've attached videos of it at low and high RPM. The impeller was replaced late last season, do you guys have any suggestions where to start looking next?

1600 RPM:

2800 RPM: