If these are 1.6 gal toilets the first thing I would look at is the water level in the tank.Shorting these toilets by even a pint of water can cause a poor flush.Check the refill tube for proper flow and placement.Make sure the shut off valve is opened all the way.If all of this is o.k then you may have to remove the toilets to check the flange for problems.There is the chance that your toilet is junk like alot of other 1.6 toilets.