Coincidentally, I just took a four hour class last weekend about cleaning and maintenance of featherweights. Our instructor refurbishes and repairs of sewing machines and re-sells them; he specializes in featherweights. Rather than taking apart your tension disks, he suggests flossing them with waxeddental floss. Skipping stitches heattributes often to either the needle’s being dull OR its being incorrectly installedwith the hole facing front – the flat part of the needle should be on the leftwhen you insert it, and you thread from the right to the left. If, after doing these two things, he suggestsre-threading the bobbin in the bobbin case before adjusting the tension.