Take the lid off the tank and check the level of the water. Is it even with the level indicator on the back of the tank? If not, your flushing action will be decreased. If this is the case, you should adjust the water float valve to give the proper level in the tank. If water is at the proper level but the flush is unsatisfactory, your flush valve (flapper) may be improperly adjusted. Play with the lever to chain length to cause the flapper to open more fully and allow more water to enter the bowl.