I know this should be under Vintage Machines but it's not a choice so hopefully it will eventually find its way there.
I recently bought a 99K and love it, but when I sew on it, it pulls the bottom fabric up ever so slightly into the stitching. I have tried adjusting the tension but that doesn't seem to be the problem. Does anyone have any other suggestions? It runs beautifully otherwise and I really don't want to have it serviced right now unless absolutely necessary. Thanks.

If you have fabric that's puckering, it's a tension issue. My 201 did that when I first got it, even tho the stitched were locked between the layers, I got a lovely, slightly gathered seam which was NOT my objective! ;)

Refer to your manual for adjusting the tension...

It sounds like the bobbin tension may be too high for the thread in use.

Turn the adjustment screw on the bobbin case counterclockwise about a quarter-turn at a time, testing after each adjustment until you get a nice smooth seam with even stitches.

You may then have to adjust the needle thread tension downward so as to balance the tensions and create good lock-stitches. :)

Thanks I'll try the suggestions.