Cannot load media. Well built on motor/controller. I had problems but it was my fault. I figured it out and everything works correctly. But if you need support. There is no phone to call. Only contact Kunray via Revain messages and useless. 06/28/2020 . Accelerate up to 41 km/h in a kart. I love the sound of this engine. Total weight with driver approx. 300 pieces. hp Note to those complaining about the motor/controller. By default, the motor only runs at medium speed at 80% power. Starting the engine with 100% full load. You need to install a speed controller (costs $10 on ebay) 1 = low power at 60% 2 = medium power 80% 3 = high power 100%. The standard motor is a soft start controller. To get hard start you need to connect the 2 white wires together to enable hard start. As of 8/20/21 the kit still works well with a maximum battery voltage of 57-58 volts from a 48 volt power supply. Most fully charged 48 volt batteries have a voltage of 54 volts.