Don't forget the simplest things first. 1997 Fourtrax300FW was running fine, stopped it to split some firewood, wouldn't start back up, plenty of fuel. I pulled the sparkplug, zero spark. I read a couple forums which made it sound like the most common problem for no spark was the CDI. From a YouTube video, I followed the instructions and used the multi meter Ohm meter to check the resistance on the two coil leads and the reading was about 0.8 as expected for a good coil. Ordered a CDI, replaced it, still no spark, but when I was checking it I noticed I was getting a shock holding onto the plug wire. Used a multi meter to check the spark plug (from instructions on YouTube videos) and there was no continuity on the spark plug. Replaced the spark plug, turned the engine over with the plug grounded to the cylinder head, visible spark. Then reinserted the plug, and it started right up.
The moral of the story, if you don't have a spark, you may want to check the plug, or replace it first. That was the cheapest option, and it would have saved me the time of pulling the front cargo carrier and plastic off to get to the CDI. I hope this helps someone else down the line.