I have just bought this motor (1993 150 V6 2.0 Black Max) and have been unable to get a tell tale with flush muffs on or in a barrel of water.  There does seem to be water coming from two holes directly above the hydrofoils and tell tale has cold air coming out from it.  I will try to put in the water and check again but was wondering if anyone could give me any suggestions.  I was under the impression that the engine was running fine for previous owner so had not thought about changing impeller.