Used this on my Razor MX650 and it worked flawlessly. Tons of torque and speed. A week or so after i built it, the throttle broke but when i reached out they were quick to respond and send another one under warranty. everything worked great from there. about a month later, a magnet in my motor shattered, but i contacted them and they were quick to respond and are currently sending me another motor rotor to fix it. love the kit!