I had changed the machine to 3 thread threading. I'm now trying to change it back to 4 threads with the second needle. It's difficult to see exactly what to do in the directions. I did it and it sews, but the 4th thread comes out totally separate on the material. Shouldn't it be combined in the chain, or does the 4th thread stay separate from the chain? Also, when I threaded the 4th thread through #6 in the manual ("Lay the thread in the notch on the thread take-up lever"), I put it through the tiny hole. Is that correct? Thanks, I'm obviously new to this machine and sergers in general.
Be sure to thread your machine in the order recommended by Juki. UPPER Looper First, LOWER Looper second, then the needles.
Here is a link to the threading instructions that you can view enlarged on your computer.
Juki MO 644 644D Sewing Machine Threading Diagram
With some sergers, but not many (singer 14u64 comes to mind), the top of the stitch will be an overedge that mates with the right needle thread, and the left needle thread will appear as a separate straight stitch. When you look at the underside of the stitch, the overedge will go all the way over to the left needle (the full width of the stitch). This is normal if you have this type of machine. Another stitch some sergers do (2/4 thread sergers) is a 2 thread chain thal looks like a lone straight stitch on both sides, and a 2 thread separate overedge.
As far as the threading of the takeup, it totally depends on your model. Always post your model number when you have questions as sergers vary greatly in design.
Usually answered in minutes!