53 and ride a 565 twister motor could not happier when I am sitting the bottom of a tree shot. I mean the ones that you have to turn the banshee around by hand.
If the banshee is a 95 or newer it will not rev if the parking brake is not fully released. Also if there is to much play in your clutch lever it will not rev. Just something to check.
It has been my experience when running race fuel the plug should be powder white color. I would call your builder to check for sure. Sorry about the motor.