What tires are they? The first issue that comes to mind is using s 30mm axle in the sr class. Is also makes me question the kart. Is it a kart designed for sr weight? Typically softening the kart would be recommended to reduce grip, but this kart may be too soft already.
Oversteer on exit seems to be the opposite of having too much grip. Widening the rear would make that issue worse but it would help if the kart was actually too stuck.
Give me a little more of the whole story and I can give you some advice on how to correct it.