Primed With Zinc Chromate
I’ve tried many primers on copper over the years and settled on Zinc Chromate. Moeller is about the only one left making it in readily available spray cans. The part number for the Moeller Zinc Chromate spray paint is 025472.
IMPORTANT: Zinc Chromate primer is not good for you. Be sure to use it carefully, in a well ventilated area, and please use a respirator.
After the zinc chromate paint the HX your engines color and re-install it.
Good luck & happy boating!