I tried this trick on my SewQuiet 4000 today, and I can confirm that it works. The Enduro brand motor in SWFLholsterīs video seems to be a lot more sensitive than the SewQuiet 4000 though. I tried it the way shown in the video with just a paper and some gradient from a pencil...it didnīt work because the light from the sensor was too strong. Then I took the thin cardboard from a pack of cigarettes...that worked better but not as good as I was hoping for. I was surprised when I saw the light right through the cardboard...must be some kind of laser-light I guess??
I ended up taking this cardboard and then started to laminate it with the sticky end of Post-it notes, sort of staggering the Post-it notes so the whole thing became thicker and thicker to one side...that worked, and I was able to fine-tune it too with the pencilmarks. The way it seems to work is that when the sensor gets light no current is passed to the motor, and when you start to shade it of gradually, more and more current is passed through it.
It worked and now I have adjustable speed through the whole stroke of the lever. But just as SWFLholster says...you have to experiment with the paper thickness/gradient a little to get it where you want it.
Thanks to SWFLholster and DDAHL for sharing this trick.