The brake rod adjustment will change where in the travel not how fast. Most use the top hole on the master cylinder arm but you might try the next hole down although I can’t believe this would be necessary. You might need new brake pads or shims for worn pads or it could be the wrong rotor assuming you have all the air bled out of the system.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience