When I flush the toilet, the flapper raises to let the water exit the tank, but won't go back down. It apparently has nothing to do with the chain length. It just seems to be weighted so that it stays open (I don't think that adding weight will help). What can I do to fix this? Thanks!

I do not like this kind of flapper because if you operate the flush handle too quickly the flapper can open too far, past its perfectly vertical point and be "too open" if you can picture what I mean. I would spend the $3 at a home center and buy new neoprene flapper

All replacement flappers have a ring for flush valves that don't have hooks.(see image) If you have hooks on your flush valve( the opening the flapper seats on) and fail to cut the ring out the flapper will not sesat correctly and give you the symptoms that you're receiving. Could this be your problem? Regards. Tom

Thanks for responding. I don't have any ring to cut out, so that isn't the problem. It also doesn't matter how slow I pull the lever. As soon as the flushing starts, the assembly goes all the way back. It is quite back weighted (the center of gravity is behind the hinge pivot point when it goes all the way back), so it won't fall forward again. If I jiggle the handle after the tank has emptied, it will fall forward and the flapper will seat. Any other ideas?

Then let's adjust the flapper. 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. 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 and let me know if it works for you. Tom