I have a Tin Lizzie 18 LS and had the same issue every time I set up a new project. I tried to problem solve by checking the timing (lots of effort and scary in case I could not get it back together properly) and ratcheting up the upper thread tension. Neither of these helped.
Turns out that with each new project I changed the needle. It is very important to get the needle in correctly and facing forward. Because the shank is totally round rather than flat like in my other machines, I had a really hard time getting it in the correct position. I could identify the side of the needle with the scarf (indent) but could not get the eye to line up properly. I spoke to my dealer and he said to use my jewelers needle nose pliers to hold the needle in place while I tightened the screw. This has worked well for me.
I hope this helps.