I've seen a lot of posts lately regarding the adjustment of the main clutch spring.
I had one engine last year that had a REALLY tight clutch, (At the lever), due to the fact that during assembly the Chinese ran the preload nut down too tight!
I posted a thread on "how to" remedy this problem...external adjustment of the primary clutch spring
99.9% of the time; this adjustment is fine from the factory!
The spring is a high rate spring, which means that very little adjustment is needed to correct for a slipping clutch, or one that is excessively tight. 1/2 - 1 turn is usually all that is needed!
It is important that the spring rate is set correctly...and again 99.9% of the time it's right from the factory.
Norman did a good job of expanding on my original post, but this IS NOT something that should be messed with in general.
I posted this information to help out those who had clutch problems beyond the normal.
If you have broken a clutch lever or cable, it will help to loosen the tension on the spring.
If you have added a tuned pipe, or other performance mod...you may need to tighten the pre-load a bit.
Use good judgement...adjusting the tension of this spring should not be done until you have a full knowledge of the clutch assembly in these engines.