Polaris predator 500 Is there a way to reduce speed/power?

Ive attached a video, but you can do this mechanically by adjusting your throttle linkage(but it may not be enough). I'd suggest making a "stop" or a mechanism to physically stop the throttle from opening up on the engine end at the carburetor or throttle body. You must add something to interfere with your engine being able to "open up", I'd reduce it so that it only opens up 15%-20% which will severely limit performance.

Another option is to add an aftermarket Rev Limiter like a MSD unit, or find any rev limiter compatible with CDI ignition and a Single Cylinder, that'll work and you can limit it to whatever rpm you prefer at the turn of a dial! I had to do this to a motorcycle and a drag car and used a simple adjustable rev limiter to keep others from mulling themselves or blowing my motor up!