So after adjusting the valves on this little ATV, I started getting an issue where the engine would just turn off after getting warmed up sometimes. If you tried to start it again, it wouldn't work until it cooled down for a bit. When this occurred, I checked for a spark (new spark plug too) and found none. It sort of drove me nuts with how random it appeared to be.

I took out the multimeter and started testing the ignition coil, pulsar coil, stator, battery, and they all checked out fine (no tool to test CDI properly). However, after a bit of reading, I started to suspect that the issue was with the pulsar coil (the sensor that reads the position of the flywheel and sends the signal to fire the spark plug). I ended up replacing this part, even though it tested fine, and this problem has gone away.

Just a heads up if anyone encounters a similar issue on the GY6 and their pulsar coil tests fine, it may still be faulty. (Though if that wasn't my problem, my second guess would have been the CDI.)

 

Yes, with electrical problems that only occur when an engine is hot, it is often the pulsar coil or the exciter coil that is the problem, they get hot first, being in the engine, but will only test "bad" when the fault is on.