I tried out my 15-91 last night. Couldn't find where I put my replica owners manual (just got it a couple of weeks ago) but still managed to change the needle & get the machine threaded. Did some stitching...and it looks like crap (pardon me). Fiddled with the tension a bit but was afraid to adjust it too much without the manual to refer to. So guess it will have to wait until I find the missing manual. Bummer.