I haven't used one myself. But for motorcycle lovers out there, I have one suggestion. You may look out after a mechanic or a person who is really involved in things such as this. I am not pretty good in combinations like this one.
My understanding is that the controller must be rated for 36v if you want to use a 36v battery pack. That is because the controller prevents the batteries from being drained too low and the engine from being overheated. I don't think the voltage matters to the motor. If the motor is rated for enough watts, like 500w, it will handle 36v without burning up.
-If you change the controller to a 36v model, I would change the throttle as well. Throttle for 24 and 36v controllers are often different.
-Lastly, you need a brushless motor controller for a brushless motor and likewise, you need a brushed motor controller for a brushed motor.
This site sells a lot of controllers: https://electricscooterparts.com/speedcontrollers36volt.html
I build motorized bikes for a living, used to. I want an electric, but 400.00 for a kit & battery seems darn expensive. Are they worth it. I am a serious rider, sometimes 30 miles a day. Ideas?