Hi there, It was me having all the problems with the thread bunching up.
It wasn´t the bobbin size though as I only have the three that came with this machine. what casued the problem was in the computer brain, somehow a couple of the minus numbers had got switched, probably me in a temper. Have made it better but its still not quite right, I have cleaned it., changed the needle, even held it upside down in case there was something gotton underneath. Think I will take it for a service. That should be fun here in Spain trying to explain... LOL, he probably only deals with the hand wheeled type. Some of them come out of the ark :D
However they do the job better than mine at the moment. Elle