Thanks for the interesting info mate. I am not surprised that you have not had a lot of response because a lot of people don't even bother changing their fork oil regularly, let alone playing with their valving themselves. Besides, getting it right is a bit of a dark art learned by playing around over time. I am no expert, I have just read up a lot on suspension tuning and so what I post is not to be taken as gospel - it is merely my understanding of how suspension works from my reading and talking to suspension tuners.
What are your fork spring ratings as a matter of interest? As far as I understand this will have an effect on your valving - higher rated springs for heavier riders will need less compression damping as the springs need more energy to compress them, and will require more rebound damping as the energy stored in the springs is unloaded quicker when weight is taken off the forks. So just because the shim stacks you have mentioned might work well for your springs, they probably will not be as effective for a different spring rate.
You might want to take a look at this Shim ReStackor application for assistance:
http://www.shimrestackor.com/Code/Sampl ... rofile.htmAlso, it is good you mentioned you have used Motul 5W oil as the SAE grade (i.e. 5W) is actually nearly irrelevant for suspension tuning purposes. Instead you should know the
viscosity of the fluid at different temperatures - typically measured in centi strokes (cSt). There is a good reference of fork oil viscosities here:
http://www.peterverdone.com/wiki/index. ... sion_FluidSo your Motul 5W fork oil - I presume it is the "Comfort Light 5" rated oil - has a viscosity of 18.2 cSt at 40 degrees celcius, and 4.0 cSt at 100C. Now I believe the "Mazocchi Fork Oil" (which is not given a weight rating) is 26.1cSt@40C and 5.25cSt@100C which as you can see if quite a bit more viscous than the Motul you have used. So the less viscous oil you have used is going to flow through the valving and via the shim stacks easier than the stock Marzocchi oil which may account for your different feeling forks, assuming you are using the same clicker settings. As far as I know the clicker settings simply control the aperture (or size of the hole) that the oil flows through before being pushed past the shim stack. So, assuming you were using a clicker setting of 12 clicks out (anti-clockwise) from fully seated (turned in as far clockwise as you can go) with the stock fork oil, to get the same rate of oil flow with the less viscous Motul 5W oil you might need to have the clicker set to a more restrictive setting like only 8 clicks out from fully seated (when you have turned the clicker all the way clockwise the hole the oil has to flow through is its smallest, and as you wind the clicker out anti-clockwise it opens the hole up more to allow more oil to flow through at a given pressure).
Because your fork oil is hydroscopic it absorbs water over time, so it will get thicker and more syrup-like over time - i.e. more viscous. So that is why it is important to change your fork oil regularly - if I remember correctly the Marzocchi manual recommends every 8 to 16 riding hours which is almost as frequently as every second engine oil change. The harder your forks work, the hotter the oil will get and the more the oil will break down - so the more frequently your fork oil should be changed.
So as you can see, the shim stack on its own is only part of the story. You will need to know what spring rates are in use, the oil being used and how fresh it is, and the terrain and riding style (faster more aggressive riders, or rougher terrain, will require different valving to slower smoother riders).