Minecraft wiki entry for Pulse, associated text: This design uses a trick to limit the output pulse to a single tick. A redstone torch cannot be activated by a 1-tick pulse from exterior sources, but a torch activated by a 2-tick exterior pulse can short-circuit itself into a 1-tick pulse. To increase the output pulse to 2 ticks, remove the block over the output torch. To then increase it to 3 ticks, increase the delay on the repeater to 4 ticks.