take the cable out at the lever end and at the clutch mechanism end, spray about 300ml (or how ever much it take sto get it free'd up) of wd 40 down it and move the cable up and down inside the sheath !!
that'll clean it out, if you have any, then apply some workshop spray grease down it and move the cable up and down inside the sheath again for a bit, re connect ans it should* be like new.
Might help
* additionally, your cable might be donald ducked and need replacing, (not unsual or expensive)