Finally back from work... puhh..
To check your clutch fibres measure the hight from the clutch fingers down to the even surface below. Between 17 and 18 mm is spot on. For each mm lower the clutch get signifantly harder to pull because the lever action angle gets too low.
If you take the entire clutch pack out all the plates should measure 9,75 mm +/- 0,1 mm. For each 0,1 mm thicker the finger higth lowers 2 mm.
You will probably find that the clutch pack is too thick. This could be caused by dirty oil. Clean the plates thorughly and measure again. If still too thick You have some options to get it thinner:
1. Buy a new clutch pack. Easy solution. Be sure that the new clutch pack have the right heigth before you buy.
2. Change the steel plates to thinner ones.
3. Sand the fibres with very fine grain paper on an even surface. Cheap solution, but a bit risky. If fibre plates get uneven the clutch will vibrate.
Be sure the pack doesnt get too thin. If so the cluch will slip as Laser says
-Jan