rebuilt waterpumt not working, yamaha

[aquahauler]

I rebuilt the water pumps on my Yamaha 225 4 strokes. The starboard one is fine however the port engine pump does not seem to work. Only a tiny amount of water is comming out of the pisser and my overheat alarm went off. I pulled the unit back off and pulled the pump apart. I though that perhaps the small o-ring had slipped out of place so I re-assembled it and put the unit back on only to find it not working again. This is driving me crazy, any ideas!!!