I have a 1978 Garelli that I just replaced rubber clutch on. It starts up fine and rear wheel spins normally while bike is on kickstand. As soon as I take off kick stand and give full throttle the bike engines just revs up and does not accelerate/ move unless I’m going down hill of driveway. Does anyone know what can be the cause of this? I also have 400 ml of 30weightND lubrication oil inside. Thanks