Dw50590

Just wondering if anyone can help with my gas gas txt 300. The bike sounds like it’s slightly spluttering when Reving up. Also I’m first gear going up hills it sounds like it’s not running right, almost like the choke is on. I have removed the spark plug and it’s very sotty and black, which correct me if I’m wrong seems like it’s running rich. I have move the clip on the carb needle up a notch (now on the very top notch) the jet size are 122 and a 38 I vaguely remember but need to check. Carb has been stripped and cleaned recently. Does anyone have any suggestions on maybe jet sizes etc. all the best adam