Fuel injector-igniters with variable gap electrodes. A fuel injector-igniter comprises a housing, an actuator disposed in the housing, and a valve including a valve head operative to open and close against a valve seat in response to activation of the actuator. An electrode cage surrounds the valve head and includes at least one aperture. At least one reed electrode extends from the electrode cage to form a gap between the reed electrode and the housing. The valve head includes a magnet, such as a permanent magnet, wherein the magnet is operative to move the reed electrode toward the electrode cage when the valve head opens, thereby increasing the gap.