Clutch Help!

Here's a little modification that might help:
The clutch actuating parts, the cam inside the cover and the pin that protrudes from the center of the drive sprocket typically come very rough on their contacting surfaces. Clean up those areas of contact with sanding disc on a Dremel Tool and make sure you have removed the rough surface. I like to buff or polish them with a bench buffing wheel with buffing compound. Lubricate them well with a good quality bearing grease before reassembly.
Also make sure your clutch cable is not kinked or has any sharp bends. Long gently curves is best. Lubricate the cable inside the cable housing. That helps a lot.
Hope this helps with your problem.
Tom