Okay, when you turn that thumbscrew in the middle of the silver plate - does it make the pointer go to different numbers, 0-5? It looks like 5 will be your longest stitch - unless this is a zig zag machine and that is the stitch
width selector. If that's the case, though, it should be making zig-zag stitches. Try getting that indicator all the way to the 5 and see if that gives you a long stitch.
You should be able to turn that thumbscrew by hand, without removing that screw in the center. All the way left to unlock the lever and all the way right to lock it down. Maybe you have to push the lever on the left all the way down to F (Forward, I'm assuming) to get the biggest stitch forward, and the same for R? (Reverse) Maybe pushing that lever is what moves the little triangular indicator toward the numbers 0-5? It's kind of Greek to me, because I've only dealt with Singers and Kenmores.
If that doesn't give you a better stitch length, just keep bathing the innards with TriFlow or sewing machine oil and letting the machine run.
The feed dogs might not be coming up high enough to push the fabric as far as you want it to, but lots of times, that kind of thing breaks free with good oilings and use.