I tried this fix on a KTM 250 SX-F with a Rocket slip-on. I used the metal mesh core from a donalson-style air filter element. Very simple to make, results are spectacular. Takes some high RPM Power away, but added some low-mid torque. This is a good thing on a 250. No jetting changes required.
Very impressed, thanks.
KTM 690 R - "Its just a little crush..."