By 
Alex: I Have Excessive Vibration of the Outboard Engine
Engine vibration can be caused by a variety of factors. The most common cause is a damaged or loose propeller. The first step in troubleshooting this problem is to check if the propeller is attached securely. Examine the blades for any breaks, bends, or cracks. If the propeller seems loose, ighten the components. However, if the propeller is damaged, replace it with a new one, and then run the engine to see if the vibration stops.
