77 Merc 500 pumping but no tell tail

[hotrod53]

I’m getting a slight dribble sometimes. I have a new impeller and it appears to be pumping. I can push a weed wacker string 16” up the pee hole, it was formerly clogged by mud daubers. If we blow air in the pressure port hole near spark plug 2, we get air coming out of the copper water line and we can blow air and hear it at the prop, but no air at the tell tail.

There appears to be no water leaking inside of the cowl. Any suggestions of where it could be blocked or a method to clear it?

 

[Chris1956]

Gee, the telltale is usually supplied by a 90* elbow on the cylinder head water jacket. Pull the hose off and see the water stream. If none, you have a problem with the impeller/water pump of some kind of serious clog in the cooling passages.