I have purchased the same machine, and waiting for hubby to finish seeding so we can set it up.
From others I understand that when you lay the bobbin in your hand, pull the thread it comes out smoothly
and will just have enough tension to tip the bobbin up on your hand, not lift off. Looser than you would think
it should be. Also a larger needle is a good suggestion, I always used a topstitch needle with a bit larger eye
in my 9inch machine on the frame. The 18.8 takes the Gros Beckert and most use the 16, but some the 18.
Probably depends a lot on the thread being used. Good luck, I'm sure I'll be in the same boat soon - looking for
help.