I have to replace the chain soon on my 02 919. I need some help deciding on a few concerns. Brand, type (x-ring, z-ring, etc.), and length. I have read some forums suggesting going with a shorter (112 link) chain as opposed to the factory (114 link) chain. Also is it ok to stick with my factory sprockets for the first change. Aprox. 12,000 miles.
You should be okay with the stock sprockets. As long as you're not doing wheelies and burnouts all over the place, 12,000 miles shouldn't be too harsh on those guys. You can always check the rear sprocket for wear before deciding, though.
2002 919 40,000 miles
"racing is life...everything else is just waiting"
The links are there which should answer most your questions.
Do a visual inspection of the sprockets for wear. If you are not sure what you are looking as for help or post a high resolution photo here.