My primary machine is a 778. It gets very heavy usage. Re bobbin issues mentioned above, I have found if I remove bobbin after winding and cut start thread to make sure it is inside plastic it works better. Also bobbin area does not like lint. Every time I change bobbin I clean that area; also likes to be oiled very often especially in this South west desert. Do not over wind. Sewing Macine DR (repair shop) gave me this advise. He has not seen my machine since. Also my DH takes it apart and cleans & oils its innards. He does maintence on all my vintage machines.
Mad cow great info