Motorcycle Repair: Clutch slipping . . . or something . . ., clutch springs, yamaha seca 400

Question
I know you are not a Yamaha person, but the Yamaha guy is not accepting questions, so maybe you can help . . . I have a 1982 Yamaha SECA 400.  Under throttle at about 5000 rpm the clutch starts to slip . . . or something weird is taking place.  At about 5000 the rpm's jump to about 7000 or 8000 with no noticeable increase in speed . . . what gives?  I have installed a new cable, clutch and clutch springs and adjusted the clutch according to the manual . . . tighten the clutch rod down till it bottoms out and then loosen it 1/4 turn and tighten the lock nut . . . maybe it is not the clutch . . . maybe it is something else, but it is driving me NUTZ!  Can you help me???  Thanks!

Answer
Sorry Dan, but it's the clutch.  Sounds like you adjusted it correctly.  You may just need to replace the friction disks.  Those things wear out sometimes and need to be replaced.  If you are running synthetic oil, it can cause the clutch to slip.  At least, it did on my wife's bike.

Regards
Rich