Check the Chain
If the chain is too long or too short the flapper will close too soon also.

Check the Flapper settings (1 thru 9)
After installing a 502 Adjust A Flush Flapper or the Fluidmaster Complete Toilet Repair Kit and the flapper closes too soon, not allowing a flush to occur in the bowl, try retiming the flapper by rotating the flapper to setting 9 See Picture 1

Reset the flapper
If the toilet continues to flush weakly or you find that you have to flush 1 to 2 times more in order to clear the bowl please follow the following steps:

1. Turn off the water and flush remaining water from tank

2. Gently remove the flapper from the overflow pipe mounting posts by lifting up on each side of the flapper frame and unclip chain from tank lever

3. Pull the back portion of the rubber down and forward until the guide pulls free from the timing track. See Picture 2

4. Rotate the rubber ball clockwise past maximum after you clear the guide in the back and rotate around until # 1 is located in the very back closest to the overflow pipe. See picture 3

5. Replace flapper onto flush valve by gently snapping the flapper frame onto the mounting posts on each side of the overflow pipe, Reattach flapper chain to tank lever

6. Flush the toilet twice. The first time will reset the water level in the bowl. The second flush should be a complete flush