A usefull questions and answers board http://the-stable.lancs.ac.uk/~esarie/honda/techbrd.htm

http://www.nrp-carbs.co.uk/ Comes highly recomended as the oricle of all carburettors

And of course  http://www.sohc4.net/ For Honda SOHCs

www.CB650.net definatly worth a visit