My Big Bear would not start easy and when it did it would backfire and stall out. Checked the obvious things like valve adjustment, intake boot, plugs, air filter and carb. I was getting fuel to the plug and fire at the plug but, not enough fire. After changing out plugs 3 or 4 times, i pulled the boot off the plug again to change the plug. When i did the coupler from the boot came off and was attached to the plug. l looked at the coupler and it had threads on it. The coupler had worked its way loose from inside the boot and caused the plug to not get enough spark. I had replaced the coil last year and the ATV had been running fine. I guess i am lost at not thinking the coupler would be screwed into the boot. I was always used to seeing plug boots that had the coupler pressed on the wire. I stuck the plug back in the boot and screwed the coupler til it stopped and pulled the plug out. Got a flat tip screwdriver out and tightened it down. I put the boot back on and turned the key and the motor fired right up like it should. Bingo.....🤓