OMC Cobra Outdrive won't pull in water

[robcurtiss]

I have a 1989 3.0L OMC with a Cobra outdrive. With water-muffs on it, water is not always pulled into the system, it seemed to help when I pressed the muffs against the outdrive. I have replaced the intake impeller, which had one cracked fin. Took it to the water today, and it failed to pull ANY water into the engine (which overheated)...luckily I noticed this before any damage was done (as far as I know). I pulled the boat out, checked the impeller and it was in good shape, spinning well when the engine was cranked.

Why am I not getting water pulled in the motor? Help, please!

-Rob