My twin granddaughters have a quad bike - Quadzilla Pro Shark 100 two stroke. Had it over a year and it has been excellent. Towards the end of last year if would not start using the starter button, but would easily kick over and then start on the button. After being stood for a couple of months it wouldn't start at all. My youngest checked every connection in the wiring - cleaned it up and sprayed with WD40, to no avail. There wasn't a spark, so I changed the plug, coil and CDI. The wiring for these is idiot proof and can only be connected one way. I cannot find a wiring diagram on line.

Then the fun began. The engine would easily turn over using the button, but still wouldn't fire. If I switch the ignition to off, the quad will start first kick, but cuts out when the switch is turned to "on". When it is running, if I press the starter button, it kills the engine. There is switch on the handlebars which changes the lights from dip to full, a starter button and an ignition on / off switch. Thinking it had to be the switch, because it affected the three functions that it controls, I replaced the switch. it arrived this morning, only to find nothing had changed. The twins can use the quad as it runs, but I don't like things that don't work as they should.

If anyone is familiar with the problem or can suggest anything, I would be grateful

 

Some bikes have AC CDI some DC. In the AC CDI types you need a kill wire from CDI to ignition switch and kill switch, as switching battery power off does not stop it sparking. However there are two types of kill systems, earth to kill is by far the most common but earth to run systems are fitted to old eTons and one or two other makes, as your system has "flipped" you must have bought the wrong CDI for your bike.