Johnson 70HP black motor

It sounded more to me that there was too much slack in the control cables, and sometimes when you raise the lever on the control box, it does not return properly to the stops on the engine. That can be rectified by taking up that slack with the black plastic adjustment wheels attached to the two control cables after they enter the front of the engine pan. One is for gearshift, the other is the throttle, enough turns will tighten it up so it returns to the idle adjustment stop screw. And I have no idea what a "black" Johnson is !

 

My bad, I mis-read Mercury

 

I mean by black motor a power tilt trim start I think 2000 70 which has a black grey engine cover

 

I am pretty confident your throttle cable had too much slack. But you best get that manual and see what those screws you have been tinkering with are all about, and return them to the standard setting, before using the engine.

 

Tks I will Im so appreciative for all 4 yr help a great service you have here

 

All omc powerheads went black around 86.
How about a photo of yours