I have a 1993 Force 120 outboard motor that began to vibrate after replacing the water pump impeller. I removed the bolts to the lower unit and replaced the impeller. I spent about 15 minutes lining up the shaft with the help of a friend. The lower unit finally went up and bolted back on without excessive pressure. The motor idles fine but when I put the motor in gear and go between 1500 to 2500 RPMs, the motor vibrates. Once I get past 2500 rpms, the motor smooths out and the vibration goes away. The rubber seal was put back in when the lower unit was reinstalled. Any ideas of what I might have done wrong when I put the lower unit back on?
