In the FAQ section there is the following advice...
Uncorking the TTR250 Two freebie mods to start with: 1. Look under the tank at your throttle linkage and you will notice that Mr Yamaha installs a stop screw that limits you to less than full throttle. Adjust the screw to allow full travel of the throttle linkage but to stop it just before the throttle slide hits the top of the carb. Some riders take the screw completely out but I wouldn't recommend that.
Can anyone post a picture of the screw and its location so i can check to see if its still in place on my bike? Cheers