im assuming you have a max torque ,comet or something like it, these have six metal shoes with a spring holding them from contacting the outer metal hub until rpm's force them.the shoes making contact to outer hub is what causes the sparks,clutch should lock up after certain speed & no slipage should occur.
Beer, Sparks associated with a clutch are almost certainly caused by metal to metal contact. Faulty shoes will heat up the outer drum to a dull red color but unless the drum is getting white hot; it's highly unlikely that the sparks are caused by the shoes themselves. Look for metal to metal contact somewhere. Most likely from the metal cage that holds the shoes in alignment. Examine the interior of the clutch drum. You're probably going to find some scoring indicating that cage is making contact with the drum. Good luck. Ogy
Max Torques are good clutches. You need to disassemble and look at what's hitting your outer bell housing. This thread might help you do so
http://www.oldminibikes.com/forum/general-minibike-talk/46488-max-torque-clutch-install-oiling.html
http://www.oldminibikes.com/forum/general-minibike-talk/46488-max-torque-clutch-install-oiling.html