1978 Johnson 115 ETL, I have my water pressure gauge hooked up and working. Its a 30 psi., I have it hooked into tell-tale line , tell tale blocked off. I get 2-3 lbs. at idle and 11-13 lbs. at WOT (5100 rpms.), is this in the ball park for my motor ? I am trying to get a 17 pitch prop...