I had that problem before also. That’s why I went with one piece valve stem from Tim of CustomBrakz. Once it is set to its max performance, it’s all set. No adjustments whatsoever, so that is the thing to consider also if you choose to go that route. I like my setup. But I guess once you find that max perfomance, you can apply some locktite to grub screws, a lot of folks do that. Oh, don’t overtighten them because you will dent the stem from the inside.