which year 650's? the ealier ones upto 2000 were carb engined bikes, the later ones up to 07 were fuel injected. The model was discontinued for the public in 2007, they were still available for official use such as police forces. The 650 was brought back into production later in 2007/08 for the usa market, those later bikes use the same engine as the x bikes, i belive the official version of the bike also switched engines at the same time. Main distinction between a rotax engined bike and the later ones are that the later ones are black and the rotax engines are grey.
the 650's upto 07 used austrian rotax engines, the later models use engines produced in tawain or somewhere like that, don't know if its a licenced from rotax as it appears almost identical except for the side covers. The later engines have 3 more hp over the rotax units.
hope that helps.