Get the lead out of the floor pan. You dont want big chunks, you want small ones spread out on the seat... Not enough left side weight, and your vertical center of gravity is too low for a kid. When you went up darn near 75 pounds, the setup has to change. You need to get on the scales, and get it to 55 left. If you take a perfectly square kart, with perfect balance, the same size tires, and just add weight to the left side. Dead in the center... It will naturally start turning left. Your kart is tight on entry. And with all the steering wheel input, it is snapping loose at the apex, and on exit. Entry affects exit. Fix the entry, and alot of times, your exit problem will dissappear... Your kart is lazy, because your not transferring weight, and adding weight to the floor pan is almost a complete no no... You need to re scale, and mount your lead on the seat evenly.. Get it to 55 left, and leave your other numbers the same... Dont say you cant mount it all on the seat, beacuse ive hung 100 pounds on a seat for kids more than once... 5-7 lb chunks is key...