Pull it off, pull the cover off & you can quickly see how it works.

The 1st set of contacts closes when the throttle is in the idle position. That's the part you adjust latter, it lets the knob on the rear of the control unit control the idle mixture + it turns the fuel off above 1500rpms when you are coasting.

The 2nd set of contacts closes as you open the thottle, but come open as you close the throttle. They then go to the arm that runs like a brush over the zig zag pattern that makes the control unit squirt fuel.

When you have it apart, you can see which pins operate which contacts because it is a little circuit board. It's simple.

I'd suspect the wiring at the plug first, it moves around a bit.