I did the o-ring mod on my 250x and it worked great, the bog was completly gone. This was done after the bike was rejetted and was running great except for the little bit of bog that was left. After the success with the 2006 250x, I decided to do it to the 2007 WR250. Also after the WR was rejetted and all the mods to the intake and exhaust, gray wire, yz cam, etc. The 0-ring mod was a complete flop. The bike has less bog without the o-ring mod. The bog on the WR is not all that bad but, I was convinced that I could make the bog go away like on the 250x. Anyone else find that in some cases the o-ring mod did not work for them?