16-04-15, 09:18 AM
Try detaching it. If the cable moves smoothly and isn't showing signs of fraying at either end it's not likely to be the cause of your problem. A bit of WD40 to flush out any grit then some engine oil to lubricate it is usually all mine needs.
The things more likely to cause a slipping clutch are:
1) contamination of the plates (especially if someone has used car oil with friction modifiers)
2) springs that have weakened with age… they're a bit marginal to begin with imho
3) rust in the actuator that converts the pull on the cable to a push on the clutch rod, you'll be able to feel that when moving it by hand when you've got the sprocket cover off. It should rotate and rise smoothly without much slop. If it feels rough or there's a lot of free play the ball bearings in there may need replacing (as well as some fresh grease).