Before everybody starts burning witches at the stake what is the weight of a 2013 bike with oil in the engine and a full tank of fuel. Lets talk from a point of knowledge rather than promotional brochures. Also all those stories of bikes having broken swing arms, wheel bearing not lasting 5 mins, suspension bushes seizing, mudguards that shatter when you breath on then think what a couple of kg applied to properly engineering critical components would make to resale values, running cost etc. Every kart race I have been to had the karts weighed as they came in at the end of the race so dead easy to do - any yes you include fuel same as F1.