Dwell63:
Check your kill switch wiring first. Unplug the CDI and measure the kill switch connection in the wiring harness to ground , It must be open (infinite resistance). If it is shorted to ground then that is why you have no spark. Before measuring the kill switch wire put your quad into the "running" condition - i.e. turn on the ignition switch, set the handlebar kill switch to run, and make sure any tether kill switch if firmly seated.
Do your have a remote control module? If so try unplugging that and see if you get spark (plug the CDI back in). If the quad starts with the remote unplugged note that you will have to use the handlebar kill switch to stop the engine - the ignition switch will not stop the engine with the remote unplugged.
Here is link to site which has another take on how to do this. Rather than measure the kill switch wiring to make sure it is open, they simply disconnect the wiring which guarantees it is open. One problem with this method is that if the quad starts you will have no way to shut it off. You can't safely hook the wire back up while the quad is running because the CDI puts out high voltage on that pin.
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Also I think there are more measurements that can be done to isolate the problem further before just blindly changing stuff (in contrast to what the above link says). Definately start with the kill switch wiring. We can proceed from there if necessary.
Here is the CDI pinout: