An easy test of the governor, watch the throttle shaft on the carb. Have an assistant suddenly push the dash lever to full speed.
The throttle should instantly turn to the wide open position then modulate back to the governed speed.
If it doesn't fully open, there is a governor problem.
If it opens but the RPM doesn't respond, there is an engine performance problem.
If it doesn't fully open, or the RPM doesn't come up to 2200 or so, possibly the U clamp (35) has slipped on the shaft (26).