I have been making a top (knit and woven) on my 10 year old Pfaff Classicstyle 2027. It has been sewing beautifully - straight stitch and zigzag - but as soon as I put the twin needle in it goes to pot. If it doesn't jam straight away it sews a few inches with great loops of thread on the back and then grinds to a halt.
I have threaded and rethreaded, following the manual to the letter. I have redone the bobbin and cleaned out the fluff - when it grinds to a halt it seems to be because some of the loops have got jammed in places where there ought not be any loops.
The tension is fine for normal sewing, and this seems to be way beyond a few loops being caused by slack tension anyway.
I have done my top stitching with two lines of straight stitch, which is perfectly satisfactory, but my eyes haven't uncrossed themselves yet.
The twin needles have worked perfectly before now (although I do now remember that I had this problem last time I tried, and I then switched to my other machine. I don't want to have to do that on a regular basis though.
Has anyone got any ideas as to what is going wrong?