You can't overtighten the clutch springs so that's not it (well I guess if you snap or strip the bolts then they are overtightened).
I adjusting the clutch would be the first step. The last Yami I had that did the same thing ended up having a broken adjuster arm. I had the clutch cover off but the adjuster was too tight and when I put the clutch cover back on it broke the arm.
1984 Yamaha YT 60 Tri Zinger(current project)
1983 Yamaha YTM 200 (rear suspension kit)..... long term project
2004 BMW R1150R
1972 Honda CT 70
2007 Lifan 110