A mixing block to supply a throttle-able hydrogen and air mixture to an internal combustion engine includes a bore through the mixing block between an air intake side and an engine intake side. A slider chamber is disposed orthogonal to and intersecting the bore, where the slider chamber houses a movable slider biased to at least partially block the bore but throttle-able to overcome the bias and reduce blockage of the bore. A jet chamber is disposed parallel to and intersecting the slider chamber and extending away from the slider chamber a distance sufficient to accommodate a shaped needle, where the needle is connected to the slider on one side such that the needle moves within the jet chamber as the slider moves in the slider chamber.