Setting the trimpot and the external sensitivity knob for this pedal can be a bit tricky, especially if you have high-output pickups, like some hot humbuckers or active pickups. If your sens knob is set too low, the pickup signal may be overpowering the effect. It took a bit of tweaking for mine to do what I wanted it to do... and even now, I use it with the sensitivity set between 7 and 8 o'clock. You'll probably need to run the sprocket before any drives, boosts, etc.
You should be able to tell if it's working by holding a sustained single note and seeing if the note dies earlier than expected. If the circuit is working, you should hear the note fade out (just like the fade in) as soon as the output of your plucked string gets below the threshold you set with the sens. knob.
Hope that helps...
use the copper brillo pad to rough up the "scrote" to ensure good contact