I had that speed problem with my Featherweight, but since William did the "fixin'" I don't remember what had to be done....it's here on the board, I *think* in this thread!
I had that problem with the "stop action" knob not kicking the needle "out of gear" with this new handcrank. For that one, thanks to a lot of great advice, was fixed by taking the handwheel off, cleaning, oiling, and flipping the washer over before reassembling it.