difference between the top and the bottom of the carburetor pistons. This pressure difference raises and lowers the carburetor slides, increasing or decreasing engine output accordingly. Post-1979 models use smaller Mikuni CV carbs with needles that seem to be listed in parts menus as being 'fixed' position,(in other words a needle that may only have one clip position). The pilot and main jets can be changed for different sizes. If the CV carb needles only have one fixed clip position. Ignition The models up to 1979 use points ignition. Two sets of points are located on the upper left of the cylinder head. On the right side cylinder head, an advance mechanism is located. An advance mechanism is used to retard the timing for easy starting and smooth idle. Post-1979 models use electronic ignition systems. Performance Cycle World tested the XS650 in March 1979. It ran the standing-start quarter mile 13.86 seconds with a terminal speed of . The motorcycle's average fuel economy was See also Yamaha XS750 Triple Special Kawasaki Z750 twin Honda CB650 References External links XS650 Standard motorcycles Cruiser motorcycles Motorcycles introduced in 1968 Motorcycles powered by straight-twin engines