Most 3W ignition problems are in the plug cap, the spark jumps inside instead of going to the spark plug...The sensor on a 3w is just a small metal pin with wires wrapped around it, nothing in there to go wrong unless one of the wires is broken....
It takes some rpm to actuate the ignition, just slowly waving a magnet across the sensor won't trigger the circuit like a Hall effect sensor..You can take the plug cap off the end of the wire...There's a piece crimped over the shield braid under the heat shrink, and the wire will unscrew out of the cap...The piece crimped over the braid can be spread apart and re used..
Cactus Aviation sells new caps.........