http://www.quiltingboard.com/t-43881-1032.htm

This Singer, the drop feed dogs is the lever on the lower right. All the way to the right, is engaged, middle is the plate raised for no feed dogs, to the left is to remove the plate entirely.

Can't on the 99 either

if you can't drop the feed dogs then cut a small piece of plastic and punch a hole in it and tape over the feeddogs or a 3.5 card