I dont know if you saw my post in the LT 80 thread.  I test rode a 2005 KFX80 with a FMF and that thing was way too peppy!!  just about pulling wheelies when it hit on power band.  Cant imagine how fast itd been with a rider that weighs 200 pound less.  plus when i tried putting around it kept fouling out the plug. 

I think I maybe found a 50...  he will get an 80 in a year or two