Please correct me if im wrong...

If you have a very rich ran carb --> issues such ass misfires occure from build up On plug. Good thing though when you air mixture screw and even pilot screw are rich is better starts.
Lean carb will cause bad starts and lack of power (more issues) but if you correctly adjust it like have a richer mixture for the cold start but not too rich that when it gets hot it wants to die. And have your main jet and needle run a bit less rich then you pilot. Should fix the issue. Like it mine it started fine, spitted alot at me and all i did was change the pilot now it idles fine.
I do have a question.... Even when i start mine up, and let it set (or not) ill let it idle with choke for a min and take choke off itll sound almost like someone is giving throttle and letting off every 5 seconds or so. I just figure its an old atv lol.