If installing a motor with a different RPM than the original motor the gear ratio may need to be changed by installing a different size wheel sprocket so the new motor can run at its fastest speed so it does not lug. The EcoSmart scooter's top speed with its 500 Watt motor is 20 MPH. A 1000 Watt motor can be geared for a top speed of 30 MPH. We have a gear ratio calculator that can be used to determine the sprocket sizes needed when installing a different motor so you can make sure that the sprockets are available before ordering the motor. Here is the link to it: https://www.electricscooterparts.com/motorwheelgearratio.html
Most 1000 Watt motors have sprockets for 8mm chain, so the motor sprocket may need to be switched over to #25 chain or the EcoSmart's wheel sprocket switched over to 8mm chain. 1000 Watt motor wear out #25 chain quickly so we recommend using 8mm chain with them.
Please let us know if you have any questions.