Exhaust studs just spin

[davedidit]

I have an exhaust issue with my Taotao EVO 150. It seems as if the threads where the studs are screwed into the block are gone. I can't get the studs to screw in properly, they just spin and spin. I was told by a motorcycle shop to use J B Weld on the studs, screw them in and wait 24 hours before putting the cap nuts on. That worked fine to actually tighten the cap nuts, but it lasted less than a mile till the studs dropped out again. I was wondering if I should try tapping the bolt holes hoping to "re new" the threads. I'm probably going to have to have someone weld the studs onto the block and go from there.
I was wondering if anyone else had this problem and what they to to fix it.