if the back wheel and chain are moving when you pull the bike cord to start it is probably a spring come off the central fugal clutch so undo the four bolts around the bell housing where chain attaches and underneath is the clutch , should be 3 springs re attach spring, if spring broken u can buy new ones or a new clutch for £10 on ebay, to remove cluch undo center bolt and prize off with some force. hope this helps
darren smart
January 2009