Your description made me think you have a tension problem and one review on the website reinforces it - see below.

It works but it takes awhile to get it to!
4 years ago I received the Janome MyLock serger as a gift four years ago. It still runs fine, I haven't had to have it repaired and it still looks brand new, after fairly regular use a few times a month. The main problem I have with it is that I have to fix the tension on at least one of the threads EVERY time I sew with it. It doesn't matter if it's just been sitting covered on my desk, I have to fiddle with the tension every time I sit down to sew. I know that sergers are infamous for being hard to thread, but this one is the hardest one to thread I have ever come across! It's nearly impossible to get one of the threads through without having to stick a needle into the tight space and wiggle the thread through. It also was supposedly "ready to sew" the first time it was used; that was a joke, it took me months to finally have time and learn how to use it and it wasn't threaded right so I had to redo it. When you finally do get it threaded and the tension right, it runs like a champ and does a great even stitch!Less
icecreammom · Reviewed on viewpoints.com