#3 PostAuthor: pertonpc » Mon Aug 15, 2011 1:17 pm
According to the parts book the silver one was first fited to Z1b so he would be right to say black painted version for earlier bikes.
However in real life I think the last few Z1a's could well have started to fit the later silver type if stocks were changing over at the factory. Go for black if you want to please the purists, but bear in mind some on offer are repro not genuine parts - so check which you are getting. If your bike is non standard and you are going for performance then pingel after market petcocks are popular and give a better flow. e.g. check out Z1 Enterprises website in USA.