Marcelino's cam mod, aka MCM.
First of all I am not a mechanic and you should check all parts and torque specs for your specific model yourself. I am also not responsible for any injury or damage to your vehicle of you do this.
This mod SHOULD work for all KLX 250 models from 2010 and newer, as well as select KLX 300 models. I am not sure which ones so check for yourself. If you have a carbureted model, you'll need a rejet to get the benefit of this mod.
You will need size 8mm, 10mm, 12mm and 17mm sockets, and probably a 8mm open end wrench. A small extension, a spark plug socket, and a 5mm Allen wrench. You'll also need some non permanent lock tight, and liquid gasket like permatex ultra black
I would recommend also havening a small torque wrench, a 8mm Allen socket, feeler gauges for your valves, a wire brush and a spark plug gap tool. Might as well get a new spark plug too. Consider getting a new valve cover gasket and new O-rings of needed.
Thank you to Marcelino for coming up with this mod, and Klxster and klx678 from the kawasaki forums for putting together the guides below.
The kawasaki forum is a great resource
https://www.kawasakiforums.com/forum/klx-250s-71/
Two helpful guides down below
https://drive.google.com/file/d/1ZZ1aERtluRT3rkYwPeQQ1M_I-Sc9akEP/view?usp=drivesdk
https://docs.google.com/document/d/12z73YZ1ASEHT8ANx9p1LTcKXjrgPUaNqAjm3gkMeNUU/edit?usp=drivesdk