I did all of the freebie mods and still needed more power through the botton and mid. I went with the Dr. D complete exhaust system and my WR250F and it made a huge difference. I too ride tight woods and some wide open and even some motocross and is a great balance for all conditions.
I have an '05 WR250F that has the normal grey wire, throttle stop, air box and jetting mods. The bike runs great at 45 degrees and warmer temps. Anything below and it coughs, sputters ....... runs very rough. I'm assuming it is a fuel mixture issue. Any recommendations would be appreciated.