How does the 4-gear shift drum work?
The KLX/DRZ110 motor is used in Japan in a street bike called a KSR110. For the US kids bike market, the motor was detuned and the shift drum modified to prevent shifting into 4th gear. The gears are still installed in the KLX/DRZ110 motor. BBR has the correct shift drum to allow use of 4th gear. It does require completely disassembling your motor to install it.