The most common way to reduce the clutch lever pull force is to change the diameter of the slave cylinder. The force-reduction aftermarket slave cylinder replacements offer around a 20% reduction but at the penalty of needing a longer clutch lever pull to get full disengagement.
Another approach to reduce pull effort is to reduce the force pushing the plates together. One way is to change the stock springs to ones having a lower stiffness. Another way is to reduce the number of springs from six to four. This gives a one-third reduction in lever pull as well as a one-third reduction in friction force in the clutch. Depending on the particular bike’s torque output, you might get slippage, but reports from owners say this approach works fine.
At least for awhile ...
Keep in mind that the force between the plates is determined both by the number of springs and the spring preload. Since preload is determined by the stack height, as the clutch friction plates wear the overall stack height decreases and consequently the force between the plates decreases.
So, decreasing your clutch lever force by removing springs will work for a new clutch but as the plates wear you will experience slippage (and accelerated plate wear) and it's likely that you'll have to put them back in to get full mileage out of your clutch. The best way to test for clutch plate slippage is to apply full throttle power in top gear.
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