i have a 1984 Riva 180 with the same problem, i replaced the friction plates and bingo problem solved. only problem is I put the clutch back together incorrectly and the 6 springs on the clutch got destroyed. now my scooter cannot come to a stop with out dying. I need to find replacement springs ASAP, this is my only means of transportation, and ive been searching for the last 6 hours online i cannot find anything.. OEM yamaha doesnt make them anymore.. someone please help!!