The bushings in that engine are not replaceable, they are put into the crankcase at assembly. If they are badly worn, you would need to repalce the crankcase and possilby the shaft. They are, however, quite durable and if treated properly will last a long time. I would agree that if you can secure the needle valve to the engine mount or the firewall, the engine should run fine as long as the back plate is still tight. You can even use a little longer fuel line between the needle and the carb if you need to in order to mount the needle.