Assuming it is a 250/300/301 rather than a 125/150.
It can be one of several things:
Incorrect adjustment at the engine end of the clutch cable.
Distorted clutch drum from being removed using a bearing puller, rather than the correct tool.
Distorted clutch plates.
Lack of end-float behind the primary drive gear. There are variable shims to correct this(if you can get them).
The first one is easy to correct if you have the manual.
The last three all require a strip down and careful examination, as per the
Hope that helps.