(quoted from post at 10:30:11 03/16/19) Easy enough to check the governor.
Take a look at the carb and linkage. With the engine off, push the dash lever to the idle position. The carb throttle shaft will be in the closed position with the idle stop screw against the stop block. Next move the dash lever to the full speed position. Look at the carb throttle shaft. It should be in the wide open position, approximately 90* from the idle position.
Next start the engine, set the dash lever to full speed. You'll need a working tachometer, but the engine should be running about 2200 RPM.
If not, the governor is out of adjustment or something is restricting the motion of the governor.
Another test, set the dash lever to full speed, start the engine. Carefully (watch the belt!) push the throttle shaft closed against the idle stop. Let the engine come down to idle speed, then release the throttle, watch what it does. It should instantly go to full throttle, then return to a mid position, maintaining the set speed of 2200 RPM.
If that doesn't happen, something is wrong with the linkage adjustment, the governor, or something is restricting the movement.
If that doesn't check out, get back with us, we can walk you through the diagnosis and adjustment procedure.
There are many things that can cause loss of power other than the governor. Once it's function is verified, then trouble shoot the other items, such as restricted air cleaner, fuel mixture, ignition and timing, valve clearance, compression, etc.
Let us know...