When did you change the brake fluid? You should do it at regular intervals to keep brakes in shape.
Dismount the brake systems and clean and replace the gaskets so you always know that your brakes are performing at 100%.
The brake is at least as important as the throttle.
Xeramic Brake Fluid is a DOT 4 oil.
DOT 4 is also glycol-based and suitable for brakes and gaskets that are intended for it. (For the vast majority of karting brakes uses DOT4)