If no pee-stream, change the impeller! Then you have a baseline. You will need to replace it in about 5 years, unless you are in sandy water or run it out of the water and burn it up.
Well what do you know. Even I get lucky once in awhile. Cleaned out the intakes and the outake and now she's pushing lots of water! Running quiet and smooth too. On to other projects. Like getting the Crestliner ready for it's inaugural splash. Think I will put an impeller in that one though. At least with the Merc I got a FSM.