I just bought a boat with a 2005 Mercury 15 4 stroke, and it vibrates noticably at idle up to around 1,500 rpm, and then is smooth. I pulled each plug wire off, and it runs the same on either cylinder. The motor starts, runs, and idles good except for this vibration. It make no difference if it is in gear or not.
Is this normal, and if it isn't, what could cause this on a otherwise smooth running motor?
Is this normal, and if it isn't, what could cause this on a otherwise smooth running motor?