Have a 1984 rd50mx that I have stripped and rebuilt etc, I didnt replace and clutch parts as they worked fine and the friction plates and springs appeared fine.
Engine runs great, but engage 1st gear and the rear wheel turns slowly and can be stopped easily by hand.
The only 2 things I have not done were:
1 didnt use a torque wrench to tighten the clutch springs - just used a good sense of feel.
2 I didnt use the oil stated in the manual as 10w/30 engine oil; I used some modern scooter transmission oil from Halfords that is 10w/40.
I have checked the oil level twice and it is spot on.
Surely the slight change in oil wouldnt cause such massive clutch slippage - ie non useable friction????
I guess I will have to drain and inspect for a stuff up I have made with reassembly of the clutch plates etc.