I have a 97 evinrude 115. E115eleua. Recently I noticed that even going straight the boat manages to cavitate. At least that's how it sounds. Thought it could be a weight issue. But the only thing that's changed is I replaced the sacrificial anode, it looks like a small stone. Not the anti cav plate. The old one was rattling around and the head of the bolt broke so I replaced it thinking it would fix it. Evidently it didn't. Motor has been mounted the same spot since 1997. Not an issue til 2 weeks ago. Sounds like it's cavitation, but could it also be the spark plug wires? A guy had jammed a circuit tester needle in the boots a while back and initially that's when it started. But 2 weeks ago it got a lot worse. Any ideas? Really need help!!