Flatback needles with no scarf requires very close needle to hook clearance adjustment to avoid skipping.
I have an older Bernina Machine. What needle should I use?
"That depends on what you mean by "older"! If your Bernina household machine model number begins with the digits 5, 6, 7, or 8 (Bernina 500, 600, 700 or 800 series machines) or the model 900, you should use System 705B needles, as your machine was manufactured, timed and developed to work optimally with that needle system. Using a system 705H needle will not harm your machine, but it may be more prone to skipping stitches, and it may produce less-than-optimum stitch quality. Any Bernina household model starting with the digit 9 (except model 900), 1, or 2, models 630, 640 and the new model 730 introduced in 2006, all utilize the system 705H needle system." Han's FAQ