My 660 Grizzly shut off during a ride. It was taken to my garage where I found the coil shorting to the bike frame, sparking everywhere. I bought a new coil and replaced it. It still won't start but was backfiring in the muffler. I bought a new CDI box and changed it out too. Still only backfires in the muffler area and still won't run. I took the carb apart and cleaned and checked it out, found to be good shape. I have a new plug in it too. I have spark at the plug and gas to the cyl but this thing won't start. I have been a mechanic for 35 year and can't make this thing run. Can anyone please help me out here, PLEASE

 

To me it sounds like you might have got the wrong CDI box.