The simple thing to do is to pull off the primary cover and watch what is happening by prefference with some one else doing the kicking
The method I use for adjusting latter model clutches ( not single spring ) is to put the front wheel against a brick wall, engage first gear , remove the spark plug lead so the engine can not start then give it a kick.
Naturally you should not be able to do this if you can then the clutch is slipping.
Or on a preunit bike the clutch or the cush drive is slipping.
If you are by yourself, a slipping clutch will be quietish, just making a whooshing sound and be sort of smooth
A slipping cush drive with go thump , thump as the lodes slide over each other and will be lumpy.
If the lobes are jumping over each other then the cush drive requires replacing.
The sprocket gets replaced regularly but the retainer does not so cumulative wear makes the lobes flat .