The reverse switch is located to the rear of the starter motor and about in center of the machine.
You will need to remove the side panels. It may be most accessible from the right side.

It looks like a small spark plug. It has one wire going to it. It functions by grounding that one wire to the motor when it is in any gear other than reverse. If the wire is not grounded, the machine will think it is in Reverse and the R light will be on. If that one wire is grounded, the reverse light on the dash panel will not come on. This condition will exist no matter what gear you are in. If you permorm this modification, when you actually put it in Reverse, the reverse light will not light. This is the only downside.

I put a wire from the wire that is going to the reverse switch at the point where it snaps on and ran it to a small toggle switch and then to ground. When the small toggle switch is closed the reverse switch is jumped. In this condition I never have the performance problem (but the R light can not come on.). I put the toggle switch in so that I can ride with it unjumped and when problem appears, I close toggle and the problem disappears.