I have a 60 hp mercury that I just changed the impeller and the water coming out the telltale port at idle is a very weak stream. It increases with rpms but still not a good stout stream. The weak stream is the reason I changed it out and it did not get any better. Anyone have any idea what may be the problem?

how long have you run the motor since you changed it?
it takes a good run for the new impeller to "break in" after 1 or 2 good runs it should be fine.

I would check the thermostat and poppit valve assembly for corrosion and problems. You can check the thermostat in a pan of water on the range top. Putting a little vinager in the water realy cleans it up to. Other than that I have seen several Mercs that were leaking at the waterpump housing gaskets causing this. Only other thing I just thought of, are you running on a hose or in the lake. On a hose they wo`nt pee very strong. Good Luck

If you just changed the impeller and not the o-ring seals and gaskets that could also be the cause of the continued problem.

What kind of shape was the water pump housing in? Were there any gouges or deep scratches in the surfaces? If so, you will lose water pressure there too.

I had this happen on my 50hp last spring. I took off the fitting where water comes out of the engine and it was clogged with the cotton off of a cottonwood tree. My pressure was good, but only a small stream. Got a toothpick after it, and all was fine after that.