I've had the Edison apart a number of times. There is two ( I think ) spring washers with tabs on them. One on each side of the pivot bolt for the stitch length lever. I did what your husband did, take them off, turn them this way and that and in the end it didn't make any difference.
It seems that there is something binding at a certain point in the rotation of everything. I've just been unable to see what it is.
Joe