I have a taotao 110cc atv that back fired a while back and hasnt started since. It turns over but wont fire. Ive changed the spark plug, carb, battery, gas and oil, ignition switch and swapped the cdi. It has spark, gas and compression. I cant find anything visibly wrong with the motor. Im thinking of removing the motor but before I go that far I want to make sure Ive checked everything else!

 

Very rare that you need to remove the engine to fix a problem. If you have a good spark and compression, with a new carb, it should at least fire, if fuel is getting to carb. I would check for ignition timing slipping. Is the TDC mark on the flywheel at TDC by the piston? If that is correct I would then check if valve timing has slipped, so do the timing marks on flywheel and camshaft sprockets agree? Note they will only agree once every two revs.