I have an original toilet 25 years old. It has a valve that shuts the toilet off too quick from the water pressure and the toilet bowl stays have full. I have to hold the handle half way to keep the valve from shutting the water off too quickly. Do I need a new valve? I have adjusted the chain numerous times and this has not solved the problem.
Regards

Let's substitute the word "flapper" for "valve" and we'll get back on track.
This is the flapper that you should be using on your toilet, (see image) If you have hooks to secure the flapper have you taken a pair of scissors and cut out the ring. That will prevent the flapper from closing normally. Another might be the linkage. 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

Thanks Speedball, That helps a bunch. Jim