Cable replaced. Operation is smoother but still very heavy.
Did you also lube the clutch cable? Many new clutch cables are not adequately lubed when new, and require a good amount of lube to operate without undue friction along their length.
Also, check the routing of the clutch cable/sheath, there shouldn't be any sharp routing, especially up near the handlebar. When I acquired my latest CB550, the clutch cable was routed under the left side of the bracket that supports the speedometer, instead of through the hole near it's base as it should be, and this caused the clutch pull at the lever to require a lot more hand strength. Once properly routed, the clutch felt normal, rather than too stiff as before.