To be honest, I'm not 100% familiar with it and it would require an entire book to explain.
Basically, fuel is sucked through a pump on the left side of the diagram. The quantity adjuster at the top moves an arm which moves a slider which controls how much fuel is injected. It's electronically controlled. On the middle is the cam. As the main shaft spins the cam, the cam turns the rotating motion into a back-forth pumping motion for the plunger on the right side of the pump. That pressurizes and moves the fuel into each fuel line.
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