First of all you have to understand how the govenor works. There is a set of balls on a track attached to the cam. These balls spin out when the cam spins because of centrifugel force. This force is pushing rod going to the outside of the engine in a direction that closes the throttle. The spring on the outside pulls against this force when you move the throttle higher. The balance of these two forces (the spring and the centrifugel force on the arm) is what controls the speed at which the engine runs. The stiffer the spring or higher tension on it, the higher the rpm the engine will run at. Essentially mower engines run like an automobile on cruize control. As the engine sees more load, the rpm decreases, the spring over-rides centrifugel force and gives it more throttle until the rpm increases and centrifugel force pushes harder and over-rides the spring again. It's a delicate balance.
In order for this to function correctly, you must have the shaft coming out fo the block, the lever attached to it, and the carburetor throttle shaft all in sync so they reach the travel at wide-open throttle all together. Once this is set, you can adjust max rpm the engine sees with just sliding the plate (that the throttle lever bolts) to up or down to add or decrease the amount of tension on the spring.
When the engine is off, the spring may hold the throttle shaft open, but as long as the weights inside can push it down to idle when running, it should be fine.
