We have extensively tested all currently available firmware versions for Hisun Guardian 550 and 750 series ATVs equipped with electronic throttles and Bosch ME17.8.8 ECUs. Our firmware is the only one that eliminates factory issues such as jerky or abrupt throttle response, the inability to drive smoothly at low speeds in "H" (High) range, and an overly rich mixture during warm-up. Additionally, our firmware increases maximum power and torque and raises the RPM limiter to 8,500 rpm.