Sounds to me like its the worm drive, It's located behind the front sprocket cover.
Over time, if not properly maintained they can wear.
Take a look at it and see if it's got lots of sideways movement when you pull the clutch lever, The movement should be smooth up and in movement to engage the clutch via a push rod.
That's something else you can check while you are there , the push rod , check it's clean and free moving.