Bruce-
A picture would help a lot in terms of giving you advice. However, even without a picture, I'm going to guess that some corrosion has built up on the rod over the years. Maybe if you take a piece of steel wool and buff up the surface of the rod, as well as the hole in the bracket that rides on it, the action will be smoother. Also, inspect the bracket and rod assembly to see if anything is loose or out of alignment. Then please report back. (Hopefully with a picture if you are still having problems.)

There is no way on a Fluidmaster to slow the incoming water other than closeing off the angle stop. It would be easier with a coast ballcock which is adjustible for fill rate. The bulb can be bounced around and misalighned by turbelent water. The water level in tank must also be set so that at the moment flush ends the outrushing water helps pull bulb into place on seat. The bracket which wire slides in must be alighned both virticaly and at correct height on overflow tube. Korky and others sell a flapper kit with a plastic bracket that clamps to overflow tube allowing the use of a regular flapper. Some folks have luck with those or just sliding the rubber flapper ring onto the overflow,not so easy but possible.

I don't think its the Fluidmaster valve that is causing a problem; its just the bracket binding on the rod.

As suggested, I can probably reduce the immediate problem by sanding down the rod and getting the bracket to move up and down more smoothly. However, if I have any issues with the rubber "bulb" that slides down and closes off the tank (e.g., the rubber breaks or deteriorates) I have not found any replacement item.

It might be time to try one of the newer flappers that clamp on the overflow tube. However, since the current "bulb" slides straight up and down instead of using a pivoting flapper like most newer toilets, I assume the rubber seat is also more vertical, which might affect how it seals. If I get one that definitely works I will then know which modern replacement parts I can use in the future.

Thanks,

Bruce

Personally, I would take off the tank and replace the entire flush valve assembly. But if you really need that part, they are still around for a price. (I think one of our old-school hardware stores still has a couple on the shelf.)

Here's a link.

Here is a link that might be useful: Vintage toilet parts