OK I notice a difference in the pressure going on. Wow. This is such a learning curve from the little machines I've been using over the past few years. But lots of fun.

I wouldn't remove it all the way yet. There's a long spring under it and there should (might) be a washer at the top of that spring, so be careful with the adjuster screw all the way out. Once that screw is out I use a small steel bristle brush over the threads then my thumbnail with a rag over it in the threads at the top, unscrew it with my thumbnail in the threads to clean out debris, then some oil at the bottom of it before I screw it back in. But this is usually one of the last things I'm cleaning when putting a machine back together after servicing. There is a lot to learn, but it gets much easier the more machines you clean (and you will acquire more vintage machines). Search this board, search the internet, and ask questions, people are very willing to help, and I have learned (and still learn) a ton from everyone here.

Okay, I loosened it and even noticed a bit of a difference in the foot pressure. I definitely am already wanting another machine. My cousin has a 16 I believe. Although he said the timing is off in that machine, so not sure I'd be able to fix it as he is much more savvy than I am. I am curious if I should use a specific oil. Oh and grease for the gears. I'm also going to throw all the silver bits in some polish so those come back to life again. Definitely a little project but doesn't seem like it will take long to get her back to her prime.

You should use only sewing machine oil, including for cleaning the surface of the machine. There are different brands, and I don't think they're all the same, I have no brand recommendation, I just make sure it says sewing machine oil and that it's clear. You can use petroleum jelly (I think the original formula for Vaseline) to re-grease the motor (there are grease cups on the underside). I look here for parts first:
https://www.vintagesingerparts.com/
I have no affiliation with the company. And you can find the user and adjuster's manual for your machine there.

I know what you mean. I used to go to the thrift stores and loosen the pressure regulator screws. It was fun when they had the quick release. I have done that for some of my machines. But, you have to remember to tighten it when you want to sew DAMHIK LOL,

There are manuals for free from ISMACS https://ismacs.net/singer_sewing_mac...g-machine.html and singer.com https://res.cloudinary.com/singer-se...ng_Machine.pdf There is a parts list at https://www.manualslib.com/manual/15...ger-15-91.html and an adjuster's manual at https://www.manualslib.com/manual/10...ger-15-91.html

Janey - Neat people never make the exciting discoveries I do.
Not affiliated with off-site link(s)

Thankfully the 15-91 I have just needs a rewiring, deep cleaning, and a nice polish. I did notice when wiping it down some of the decal started to fade a bit so I definitely want to learn how to touch those up later on in the future. The table is a No. 42 cabinet so I definitely want to restore the wood the best I can as well.
The grease cups are those giant black screws on the motor right?
Thanks for all the help, currently waiting on a new 3 pin terminal body as mine was actually falling apart and held together with more electric tape. I did notice the guy gave me a pedal for a 66 and not the 19-15 but I kind of like the pedal I have better.

I'm not sure I understand correctly. Are you loosening it just when the machines not in use and tightening when you use it, of course making sure the pressure is accurate for each individual fabric, and then loosening it back up again after?

Yes, those are the grease cups I'm talking about.

Basically that's what I mean. I don't sew much, but I do like to work on machines, and at any given time have a number of them cleaned up and just sitting there (currently 18 with 5 more needing servicing). A while back I started a thread about "parking" a machine
https://www.quiltingboard.com/vbulle...e-t312178.html
which might help explain my comment.

It is generally recommended on these old black machines that it should be wiped down with sewing machine oil. There are a couple of threads about it at https://www.quiltingboard.com/vintag...v-t167789.html and https://www.quiltingboard.com/vintag...s-t193635.html

That is a great cabinet. If it is decent shape, I would recommend "reviving it" by following the instructions at https://www.quiltingboard.com/tutori...s-t109859.html

Right.

I'm not sure what you mean? If the plug fits, it does not matter which foot controller (aka pedal) is used.

Yes, loosen it when not in use. You just have to remember to tighten it when you go to sew. It doesn't feed fabric very well when loose.

Janey - Neat people never make the exciting discoveries I do.