I have an 08 yz450f that I bought used from a vet a class rider. It only had 30 hours on it when purchased, of which I have proceeded to add to greatly this year. However on my first woods ride of the year, I smoked the clutch to the point that when in high rpm's the clutch would slip like it was its job. Over the next few days I tore apart the motor, took out the old clutch, checked for excessive wear marks on the basket and pressure plate, and installed a new clutch. The new clutch last about 20 hours and it gave in to the ghost too. I run slack in the lever so that the clutch engages at roughly 1/2-3/4 pull, but yet my bike burns up clutches. On the second clutch install, I opted to install a heavier flywheel, which has made the clutch last roughly 40 hours and counting. I change the oil every 6-8 hours, and oil filter every two oil changes, use Klotz MX4 oil, but at the end of the day, I strongly believe that there is something mechanically incorrect with the way the clutch operation works on my 08 450.
I figured it was a pull ratio problem, so I tried different brand cables and perches, and all yielded the same result of smoking my clutch. At the end of the day, I am very happy with the bike and the addition of a heavier flywheel. It hasnt solved my issue of going through clutches, but it has prolonged my clutch replacement by 3 times as of right now. Mx bikes are very particular beasts, and they require maintenance on a frequent basis. Some people who do not use their clutch to shift may get 100+ hours on a clutch, but I prefer to burn up a clutch than take a chance at ruining a tranny by power shifting. Just my thoughts.