Do one thing first, than see if you get any improvements.
If so, you'll know what to do if it happens again...
As far as adjusting the plunger like Pete rightly recommends, do half a turn first because I can't see going more than a full turn if no one has messed with the clutch previously or if the bike has a low mileage. If it was fine when you first had the bike, you can't be too far from the truth on that.