I’m 6’1″, 195lbs with long legs and fit in a CRG Road Rebel. It’s tight, but I have gotten used to it. I actually purchased a front porch extention, but once I installed it and sat in the kart it just did not feel right. My heels were moved higher, because they had to go on top of the front rail, and it moved the bodywork and everything else forward. I ended up getting rid of the front porch. Add around 1.5cm to the dimensions listed in the CRG manual linked above for 125cc classes, and that is right where my seat would end up. My current DR kart the seat is real close to that as well, same amount of legroom. With your weight, I’m guessing you would have to add a few lbs depending on what class you run. That should give you even more flexibility with the seat location.