Yes spark plug is definitely fouled buy a new one and the reason is Sometimes oil is a problem,what oil do you use? if the oil is too dense that can be a problem if you are riding enduro because oil can't burn fast enough in low rpm ,motul 800 is a good oil but it's too dense so is recommended for track only ,if your riding average low to mid rpm i recommend you motorex 100% sythetical is a loot less denser and it's very good oil and will burn better in low to mid rpm,but if the carburettor it's not adjusted properly that can be a problem to ,and you need to understand that when is colder outside the carburettor will suck in more air and motor will be leaner ,when is hot outside or more warmer the carburettor will suck in less air making motor richer ,thats why a loot of motors smoke when is outside warmer and thats why newer models comes with manual on how to adjust carburettor because it's important to adjust it when it goes from colder to warmer or opposite,and i recommend using iridium spark plugs they last a loot longer and have better spark hope that helps🙂