My toilet flushes fine, but the bowl does not fill up with enough water. Sometimes it fills up with more water, sometimes less, but on average it seems to have about half of the water that is should. I thought perhaps the flap needed to be adjusted so it would stay up longer, allowing more water to flow into the bowl. I have an adjustable flap, but that seems to simply drain more water down the pipe, not put more water in the bowl. I'm stumped.