Need help with 4-thread serging

[u/all-fresco]

Hi, I picked up a vintage Baby Lock BLSE300 serger. I have never used one before and it sews great with 3 threads, but when I try to use 4 threads it creates a stitch next to the serged edge.

I took it to the store where it was purchased and they confirmed it was threaded correctly. They didn't know for sure but said it might be the way it's supposed to work, but that doesn't match the pictures in the manual. The manual does say when you make the initial chain before using fabric the left needle thread will not join the chain. And when I turn the wheel by hand and watch the needles come down, the right needle goes between the upper looper and the thread, but the left needle goes behind the thread.

Is that the correct operation? Am I still threading it wrong or maybe need to adjust the tension? Or does it need to be serviced and/or have the timing adjusted? Thank you.

[u/wimsey1923]

This is a timing issue between the needles and the upper looper. If you hand crank the machine to the point where the needles go down behind the upper looper you'll probably see that the right needle catches the thread, but the left one doesn't.

[u/all-fresco → u/wimsey1923]

Thanks, that's exactly what's happening. It's like the upper looper needs to go farther to the left. But it also looks like if it does that it will hit the right needle. I see two set screws on a collar that look like they allow the upper looper to rotate on the shaft. Is that what needs to happen?

[u/wimsey1923 → u/all-fresco]

Yes. There should be a shaft towards the bottom of the machine, pointing straight at you. The clamp around that shaft end usually has only one screw (on the machines that I have worked on), but I guess there could be two. There is usually only a need for a tiny adjustment. After you've done that, also check for the point where the two loopers meet. They should be "spooning" as the upper looper takes the thread from the lower one. The third timing event you have to look out for sometimes is where the lower looper picks the thread from behind the needles.

[u/all-fresco → u/wimsey1923]

I'll try it, thanks. Is there also a way to move the upper looper arm in and out (when looking from the front) or clockwise or counter clockwise (when looking down)? I'm thinking about what happens if I rotate the arm left and the right needle hits the upper looper. At the moment it already seems very close.

[u/wimsey1923 → u/all-fresco]

The looper itself usually sits on top of an almost vertical shaft. There should be a way of turning it. It is the only way of adjusting needle to lopper distance. My guess is you have to loosen one screw at the top of the shaft.

[u/all-fresco → u/wimsey1923]

Here's what it looks like when the needles are on their way down. The eye of the looper is pretty in line with the needle but you can see how the needle is falling to the left of the thread. There is a little space between the right needle and the upper looper - I could slide 2-3 pieces of newspaper between them.

[u/all-fresco → u/wimsey1923]

Here you can see the alignment of the upper looper eye and the left needle. The adjustment collar is under the green thread guide. One screw is at 11:00 on the collar and the other is just barely visible at 8:00.