8dn belts what's the reason?

The white tunnel will show dirt for sure, especially belt dust, but there's consiserably less with the 8dn from what I've seen, ran 8jp all last year, switched to 8dn this year
 
You can also remove the screws altogether and use an adjustment tool.

Here is a TY vendor's answer to the belt adjustment as well as aiding in belt removal,
http://www.ospracingparts.com/yamaha-sr-viper-belt-adjuster-with-float/

I bought one the week he introduced them and it has worked flawlessly and makes the belt deflection easy to set and maintain.
 
here's a pic at 700 + kms I haven't cleaned it yet
belt dust 003.JPG
 
8DN from new. 650 miles (about 1050Km). 2015XTX SE



belt-dust.JPG
 
Mine was worse than Yamamarc with 8DN and less miles. I have 500 total now. I went into a 200 mile or so jaunt with some testing and had dust everywhere including the back sides of my hand grips.
 
It could very well be slip on top.... I was having some issues with slip and I added some tip weight and unwrapped the secondary 1 and it seemed to correct it
 


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