We have a Toro 36" walkbehind with a 14 hp Kawasaki and an electric clutch. When the mower fully heats up, after about 10 minutes, the clutch disengages. I can let the mower cool down for a half hour and the clutch will work again. However, after 10 minutes it fails again. The clutch is two years old and the wiring seems O. K. Any ideas what might cause this? Thanks for your help.