First, remove the cover where the engine sprocket is and lube the end of the lever and the clutch pin with a dab of white lithium grease. Next, disconnect the cable from the locking lever on the handlebar and drip some oil down the cable. I used regular houshold oil on mine. Make sure there are no sharp bends in the cable. Keep working it and it will get easier. There are many posts related to this. Good luck!
My clutch cable was frayed inside the jacket which made it very hard to pull. I replaced it, and the junk lever that came with the kit, lengthened the clutch arm on the engine with a piece of 3/8" copper, soldered it on to the factory piece, removed the arm and pivoted it inward for an easier and smoother pull. Dax sells the extended arm if you dont want to make your own.
First thing, actuate the lever at the motor end to see if that moves smoothly. If it doesn't, follow the "take it apart and grease it" advice. If it does move smoothly your problems are in your cable.
My clutch cable was way too long so at first I rigged it with an extra loop-de-loop. Bad idea.
Then from walmart I got a universal "bike tune up kit" that has two long and two short brake/derailleur cables for $4.50! Has steel cable and cut-to-length jacket. Rebuilt the clutch lever action with this stuff cut to an appropriate length, and an old "real" brake lever and it's 400% better. I suspect the walmart cables are vinyl or teflon lined for easy sliding, but the cheapo chinese ones are not. Also the steel cables had this waxy coating I would not try to duplicate with aftermarket lubes.