You don't need a special tool to adjust the valve.
You can do it with a very long 1/4" bolt.
But, if the FPS is lower then it should be, there is lots of small things that can cause that to happen.
Like, the valve FPS adjustment needs to be set at a "click". If it is between "clicks", it will have low FPS.
If the valve screws are replaced with screws that are extra long, then you will get low FPS. If you are missing the spring guide, or bumper, or if the nubbins are bad, or if the orings are bloated, they all cause low FPS.
I wrote that massive VM FAQ at the www.vm68.com
site, though the site is run by Chris Mader. He knows just about everything there is to know.