You need to find a "buddy". Plain and simple, you have to find someone with a running banshee that you can borrow the cdi, coil and stator off of. Then, not all at once but one at a time, put these pieces on there and go ride for a bit and see if the fix is found. If it starts acting up, take that part off and swap in another part until, hopefully, you've found the issue.
Rare has a good point on the resistor plugs, make sure you take out the 7's and replace them ONLY with BR8ES until you get this problem fixed. Buy 2 or 3 sets.
Also, you need to get a timing light. Park a vehicle next to the quad and put the 12v connectors to the car's battery, then hook up the light's pickup wire to a plug wire. Try to fire it up, if it's not starting, ensure that you have light coming out of the timing light. Try the other side.
Also, check your grounds, and I mean EVERY SINGLE ONE. Check back by the CDI, then check by the coil, just check them all and verify the ground with an ohmmeter to be sure. A simple loose ground can cause severe pains on a running bike.