1. Are you getting fuel flow out of the tank? Tried it on reserve?
2. Are you getting spark?<----no spark may be caused by alot of things.
3. If you are getting spark is it stong?<--may be a weak battery.
4. Do you have a kill switch and has it been eliminated?
5. Have you gone through the troubleshooting guide on the ignition system?
Three things I would check next.....
1. TORS switch
2. Carb switch
3. CDI
The TORS switch is on the throttle housing. It's the black insulated wire coming from the throttle body itself. The switch is the little red dot that when the throttle is in the closed position it makes contact with the switch. Make sure that's not binding up and it moves freely when the throttle is open and closed.
The carb switch is located on the shifter side of the quad tied to the frame above the carb...kinda near the fuel shut-off....it's the white plug on the left of the pic.
Try and jump out the other end of the plug with a small wire. It should be the female end of the plug and you can see two prongs inside the plug.
The CDI could be the culprit.....best thing to do is find another YFZ and try his/her CDI in your quad if possible.
One other thing to check is this little wire near the negative wire to the motor..it actually runs with the battery ground. Make sure it's not corroded or unplugged.