In mph how fast will a 12hp engine go?

The speed of a 12hp engine in mph depends on various factors such as the weight of the vehicle, the gear ratio, and the aerodynamics. Generally, a 12hp engine can propel a small vehicle like a go-kart or a lawnmower to speeds ranging from 20-40 mph. However, for a more accurate estimation, a specific vehicle and its characteristics would need to be considered.