1996 or 7 Yahama gas cart
 

I bought a used cart that has the 'high speed gear' installed, it will go around 26 to 27 mph according to my GPS speedometer. My question, can an adjustment be made to limit the speed to 20 mph WITHOUT replacing the high speed gear. Also, on this vintage cart I am getting mixed info about where to make the adjustment, at the engine or at the differential.
What would be a typical cost of this adjustment?

Adjust the governor at the differential, the wider the spring the slower it goes.