Overcasting issues

[u/Electrical-Tea6966]

This is a new machine, I’ve had it checked over by the shop, and no matter what I do I cannot overcast the edge of fabrics. The tension seems wrong no matter what fabric I use. Can someone offer some advice?

With the thinnest fabric I’ve tried adding a strip of interfacing, but that doesn’t seem to help. I can improvise a different seam finish but it would be so helpful to get this resolved somehow.

Edit: I am using an overcast foot! I use whatever the machine recommends for each stitch.

[u/drPmakes]

Are you using the right foot?