The Vee Twos came with bronze friction plates, made to run dry. If you clean the plates, the clutch works ok for awhile, then gets very grabby until you clean it again.
I switched to Barnett Kevlar friction plates run in ATF.
Same as Howard, I fitted a gasket to the Clutch cover. I made the first one in heavy gasket paper. Now you can purchase much better gaskets in nitrile rubber over thin Al ( Cometic)
This change solved all the clutch problems. I've used the bike two up with luggage in stop start city traffic and the clutch never complained, very smooth and very light.
I would try that change before adding heavier springs.
Glen