I've sort of managed to fix my straight stitches on my Bernina 801. I cleaned out the bobbin race (that was oily and dirty), oiled the machine in the right places and changed my cotton and needle. I cleaned out under the sewing plate (yes there was a little bit of fluff)....I put in an old needle ( I keep my old needles) put the thread through the left side of the tension disk and now it's sewing straight stitch again! I don't think it likes my other German brand of sewing machine needles or the right side of the tension disk........I think the Bernina prefers Schmetz, better yet Bernina brand needles. My one problem there is I don't know where the Bernina shop is anymore.......The city is not quite the same anymore!
Anyway for know it is sewing okay........but I think the machine is on it's last legs, my ruffler refuses to work with it. There seems to be no power in the sewing machine to make it go....It just whines and clacks now....my ruffling days are over for now.