This is the first time that we have heard of this type of problem with the Razor Crazy Cart XL so we do not know how to solve it. Since the cart is so new we recommend working with Razor to solve the problem as they have a lot more experience with it than we do.
If you find a solution then please let us know so we can pass your experience on to others who may be experiencing the same problem.
We purchased a Razor Crazy Cart XL in June 2018. We had fun on it for a few days but then the chain kept coming off. I've sense taken it apart and tried to fix it multiple times. The tensioner doesn't keep the chain tight. The kart rides fine when going straight and making wide turns, but throws off the chain when trying to drift or make sharp turns. I ordered a new tensioner and a new chain and I'm still having the same problems.