How do I fix a toilet flapper that closes too fast? I've replaced the flapper and adjusted to all the different settings. I've also varied the chain length for the flush. Nothing works. There is some sort of water saving device in the toilet, similar to a milk jug (but not, it's a commercial-type thing) outside the flapper. What should I do? Thanks.

Make these adjustments, if you still have a problem get back to me.
With the flapper seated the linkage wants to have 1/4" of play. Too much play and the flapper doesn't get pulled back enough giving you a short flush. Too tight and it lets water seep past the flapper. I adjust the chain by the link and if it needs fine tuning, I bend the flush lever rod a bit until I have the desired play in the linkage. One more thing about a flapper. You will see where the old flapper hooks onto the base of the white overflow tube. On a older type with no hooks the flapper has a ring that slips down over the overflow tube to the seat. If your tank has hooks, take a sharp knife or scissors and cut the neoprene ring off on the marks provided and hook the flapper on the hooks. Leaving the ring on will interfere with the flush The water level in your tank should be 3/8 to 1/2" below the top of the overflow tube when the tank's filled. And the little tube wants to run from the ballcock and connect to the white overflow tube. Good luck, Tom