I had a 1997 175 HP johnson rebuilt last fall. It has a 14.5 x 19 aluminum prop on it, and the engine is mounted on a 2,100 pound 20' center console.<br /><br />I followed all of the break in rules. After putting 10 hours on the engine, I finally took her above 3,500 RPM's. At this speed the engine was making a rather loud vibrating like noise (by the way this was in June of this year). I could get up her up to 4,500 RPM's. Other than that the boat ran fine. I take her down below 3,500 RPM's and the noise goes away.<br /><br />I called the guy who rebuilt it. Although it was past the warrantee period, he took it back. He said that one of the plugs had gotton foul. He replaced it along with a head gasket and said the boat should run fine.<br /><br />I just took her out again and got the same noise. I will be calling my mechanic again, but does anyone have any idea what could be the problem?????<br /><br />Thanks
