Hi Sammetje,
On the back of the machine, where on the inside you have the looper hight adjustment, there's this square bolt that is intruiging me. Have you figured out it's use?
I think it may just hold the assembly on the inside, but on my machine (a model c) it isn't firmly fixed, suggesting it's some form of adjustment.
Machine works well so I'm a bit scared to go and try all sorts to figure it out :-)
Greetz Max from Enschede