on the contrary, the clutch cable may be too loose.
when you squeeze the clutch lever, it should pull the cable, which in turn pulls the clutch arm on the left side of the engine. the clutch arm needs to be pulled far enough to disengauge the clutch.
this is a hard thing to understand if you don't "get it" or know how a clutch is supposed to work.
The arm should pull far enough to disengauge the clutch.
when you squeeze the clutch lever, your bike should roll, and when you let the clutch lever out, the rear wheel should drag or skid (with you off of the bike).
with the clutch lever out, you should be able to wiggle the clutch arm on the left side of the engine with your fingers. It shoudl just wiggle back & forth and there shouldn't be any tension on the arm.
with the clutch lever squeezed in, the arm should rotate in towards the right side of the bike, and it should be stiff, with pressure on it. you should not be able to wiggle the clutch arm with your fingers.
On the other hand, if you have the cable adjusted right, there have been cases where a clutch has gotten stuck internally. This can be caused by the engine sitting for a long time proir to it being sold. sometimes ther can sit long enough for rust to build up inside the clutch and cause it to stick.
I've never had that happen so i'm not sure how to fix it (if it is that) but i'm pretty sure that you have to take the clutch apart to get it freed up if it's stuck.