Re: Motor swap,from 50 horse to 70 horse.
How was the Merc plumbed? Give us some help here. They either pick up water pressure from a port in the water cover or via a "T" fitting in the tell tale hose. Either place works on some motors and on others not. Try the tell tale first since it is as simple as stopping at Lowes for a plastic "T" fitting. If that doesn't work you need to add a port at the top of the head. There is a post somewhere in this forum showing how to do that. Use the search feature to find it.