Bob's right, post a pic if you want specific instructions, the set screw is probably just full of road grit.
TKC-80's SUCK on the street so going with a basic tire like the Scorpion will let it ride and handle MUCH better. Don't expect it to be any lower though, the tire lugs are tall but the carcass has much less of a dome to it. The bike will be very close to the same height when you're done, but theres plenty of ways to lower the suspension slightly.
If you are swapping the wheels yourself please note to be careful and FOLLOW THE PROCEDURE IN THE SERVICE MANUAL EXACTLY. Including exact torque specs. Yes, I know it's a simple job, but Buells are weird and need it done correctly or expect imminent bearing failure.
Heres a .PDF of the service manual:
http://buellmods.com