This is my only working sewing machine. I have a second 77 I bought a couple months ago for $50, to use for parts (if needed). This is the first time I've tried using a buttonholer. My sewing career is pretty minimal, most recently sewed a lab coat from a sheet for my 3 yr old (wanted to be a doctor for Halloween).
@Mickey2
The thread I'm using is pretty thin, so I'll try some thicker thread. The sewing machine does occasionally cause thread to bunch up under the fabric, so the bobbin area may need cleaned. I agree that the buttonholer shouldn't be affecting the movement of the needle.
@OurWorkBench
With the base plate installed, the bobbin thread does not get pulled up. I can start with the bobbin thread exposed below or above the base plate, but that does not seem to matter. The attachments says "White" in big letters, but I'm not sure of the specific model and it did not come with a manual.
@lovelyl
I don't know how to verify it is the right base plate, but it does seem to fit correctly.
Thank you for the advice so far. It'll probably be a week or so before I play around with the sewing machine again, but will let you know what I find.