Check for sparks at the sparkplugs,if there is no spark check the wires back to the CDI ignitor under the driver`s seat.If you have sparks check the fuel sistem. Maybe the fuelpump in the gastank isn`t working. Another problem i can think of can be the vacuum hose that goes to the tank that switches on the fuel system. If nothing works I can suggest using an osciloscope to wiew if the ignition sensor works. it is located on the left side of te engine(as you stand on it) in the Yamaha cover.if the sensor works you might consider borrowing an ignitor from another motorcycle.I hope i helped you and I appoligise for bad spelling