I'm guessing you are refering to putting a XB9 primary gear and chain on an XB12. This yields and 11% increase in torque, of course at the cost of an 11% reduction in top speed. If this is what your refering to then americansportbike.com has them for around $200, or any Buell dealer should be able to get it. Of course this is of no use if you have an XB9.
I might just do that im having a problem with my bike at 4900 to 5000 it falls falt but if i twist it more it pulls. I read A post that had sim problems.
let me giv e my set up 2007 xb9r race ecm jardine and k&n. this started about 300 miles ago . ill be riding ant normal speed and rpm but if i hold the throttle at 5000 it stumbles sorry about the spelling. but if i give it more throttle it goes away. i HAVE NO CHECK ENGINE LIGHT or other issues
you'll probably get to much fuel round that rpm range.
if you did not have it before...a tps reset should resolve it. before doing this you could maybe try and clean the k&n filter, cheap and may help a little bit.
but reset your tps, let the ecm learn again and i think your problem will be solved.