Thanks for the advice people. I did the swap, and now own the 25 HP 2 stroke. It came with a skeg protecter on it, and I am happy with the design of it. The engine didn't seem to spit out water when the motor was first fired up, but after about 45 seconds, water started to dribble out. Then about 30 seconds later it was a solid stream, then it went back to about a half flow stream. It did this a few times. The water was never scolding hot, but it was very warm. It seems like either the thermostat is opening and closing, causing a strong, then a weaker stream of water. It is way easier to change the impeller now, and know that it has been done.
cheers.
If the motor was used in the salt, the water outflow can be partialy blocked with salt crystals.
The resistance will also cause the motor to run rough.
Take a small piece of wire and push it into the water discharge and clear it out .Then run the motor again and see if it makes a difference.
Mine was 90% blocked.
I had this happen on one of my kickers and found out first hand that this is what happened.
Easy to do.Just don't push the wire in real deep.
Worth a shot before you get too deep into diagnosis.
Rando