I use the regular needles for sewing machines, that's what my 14u64A is labelled for. I got mine used from a friend and it does everything I need it to. I think you got a great deal on a very good machine. Remember that in the 80s the sergers were still "new" on the market, or relatively so. The quality hadn't really gone too far down by then.
I don't do a lot with my serger, but I do make tank tops and serge the edges of some fabrics prior to washing and assemble the odd item with it. It does live in my studio rather than the "sewing machine repair shop" upstairs, but I don't know if I've used it since I moved into my studio in November. I think I did in October. This is why I would never buy a new one, I just don't have a lot of need for it, but I love having it when I do need it.
Threading. I fought the first couple of times, and mostly it was because I thought I would thread it the way I wanted to (using the diagrams but not in the proper order) and not in the order that the manual specified. I have a serger threading "tool set", but I agree - tweezers and a dental floss threader will do about as well. The first time I took my serger to class, the lady who ran it told me that the first thing they would do in a class given by a dealer is cut my threads and make me rethread from scratch.
I couldn't figure out how making me run out of the shop crying was going to help me use my serger....
I know a few people who run their 4 thread sergers as 3 thread all the time.
Now I thread them in about 5 minutes, and have serviced 4 of them.
Check the knives and make sure they're still sharp. They will still cut cotton OK if they're dullish, they won't cut tricot though. It probably wouldn't be bad to pick up a set to have on hand anyway, I have no idea what the availability of the knives will be going forward... it IS a 30 odd year old machine. I should order a set myself now that I think about it.
Needle plates - They share with some other brands, and I have a spare or two, if you need them, PM me. When I got my serger, some parts were missing and I replaced what I needed to make it work. About 6 months later she found them all, so there are parts here I will likely never use.
Just like with sewing machines, tension just clicked for me one day.
I think this is how it works, I will verify when I get down into the studio for sure and correct if I was wrong.
You're aiming for the looper threads to lock right at the edge of the seam with no tunneling or gapping threads.
Usually, If the thread is loose but pulled over to the back, the lower looper is too tight. If it's loose but pulled up to the top, the top looper is too tight.
Both loopers too loose can look like a frilly edge when the lower thread and sometimes the upper thread is looped and loose at the edge.
Both loopers too tight will usually tilt the stitches on an angle, and can tunnel the fabric as they yank on the needle threads.
Just like with a regular sewing machine: Needle threads too tight, looper threads are pulled to the top. Needle threads too loose, needle threads are pulled and "loop" at the bottom.
Singer has the user manuals online, that's where mine came from. They also have a really good book, part of their Singer Sewing Reference Library - Sewing with an Overlock that has excellent photos and great explanations and a few projects in it.
I also have a few books from Naomi Baker, Tammy Young and Gail Brown that I quite like.
Possibly the one I've used the most of is ABCs of Serging by Tammy Young and Lori Bottom.
These are all books I found at the thrift store.
Where did you find the service manual? Free or purchased?
UGH. Sorry, another novel.