I have changed the spark plug in my mom's 120 Chinese atv...because it was running rough ,cutting out when accelerating..sometimes would hardly move..cleaned air filter..replace fuel filter..clean spark arrestor..I think it's running rich..spark plug smells like gas n black..cleaned again..is there anything else I can do to fix it ..besides taking carb apart..it's only a year old ..I'm Leary of messing with carb...

 

The usual problems with something suddenly running rich is a partly stuck choke, or a mixture screw may loosen off. You have already sorted the air filter. Small Honda clone engines have a fairly basic carb, so you should be able to fix it, remember where each part you take off goes back and that some adjusters and jets need exactly the right size of screwdriver, or you can damage them.