My toto toilet has both 1.6 gal and 6 gal flushes. the short flush doesn't go down.

I am not a toto expert but i think i understand the gravity control toilet concept.A gravity flush tank type toilet flushes do to the force of water traveling from the tank to the bowl in a small passageway and forces the water in the bowl towards the integral trap in the toilet.In other words the water isnt dumping quick enough or the passageway is restricted.,My guess is the flush valve isnt dumping all at once.