Raw Water Flow Reduced After Impeller Change

[Howler]

Hello, I just changed the impeller and gasket in the water pump">raw water pump on our Yanmar 3GM30F. Before the service the raw water flow was great in terms of volume and frequency. After the service, it decreased to a trickle with lower frequency. I read Charlie's post on raw water flow, but am posting separately because there's such a clear "before and after" leading to doubt there are blockages upstream or downstream of the pump area.

The impeller is new and has self-adjusting blades. The belt driving the pump is properly tensioned and turning at normal speed.

Any ideas what I might have done wrong during the change leading to this reduction in flow?

A friend suggested that the system is picking up air. Any suggestions on how to test that hypothesis?

For now I plan to repeat the steps taken to see if anything turns up but I'd appreciate any suggestions. Thanks!