Possibly a tranny problem with either the main shaft or the counter shaft. The clutch itself is a simple mechanism-a handlebar lever, a cable, a pivot lever on the case that directs a small push rod in or out, a bearing, a housing holding springs, bolts and then the clutch plates and discs. So if you have lubed the cable, and it is not binding anywhere, the problem would have to be with the shaft that the clutch is connected to-usually the main shaft.
