Changed the prop to an acme 525 3 blade 1 1/8 diameter shaft, 13 diameter, 11.5 pitch. used valve grinding compound to seat it. Runs like a champ. No vibration whatsoever. I have not been able to open her up for any extended length, so I'm not sure how my top end is affected. Hole shot is about the same as before, but, like a said, i have a bad plug.