I have the viking 18x8 which is the same machine as the tin lizzy TL18. There is a great video on you tube which show alot about the machine that is not explained in our manuel. On our machine it is necessary to give the upper tension tension a good full twist. I had problems that sound alot like what you are having, it was that I did
not have the bobbin in correctly. Watch the video it might give you some good insite it sure did me. Hope this helps!!