tvhelidad, one thing you can do is to put a prop on the motor {something to hold onto} and check for wear in the bearings by holding the motor with one hand and apply pressure via the prop to see if you have up and down ,or side to side play in the bearings, secondly put a few drops of fuel down the carby and check for good compression. If bearings are sloppy, then they have to be replaced, front and rear bearings , if no compression is felt , then the motor will need a complete overhaul, so you be the judge. Just remember that badly worn bearings will explode and cause serious damage .