Here is a web site that I just love - Jenny has parts and TONS of info, a free manual AND she has parts. The bobbins I got are better than the ones from Walmart. blog.sew-classic.com/2008/10/25/singer-401-401a-403--403a--404--sewing-machine-review.aspx
If it still isn't zigging and zagging there is more info - let me know.