Looks like the carb and air filter housing are moving around. Are the carb mounting bolts tight. If they are loose will cause an air leak which can effect engine rpm.
If you disconnect the governor spring what does the rpm's do. They should go to idle if the governor is working. If it doesn't go to idle then either the governor gear is not working, the governor static adjustment in incorrect, and the throttle in the carb is not moving freely throughout its entire range of movement. Also make sure the idle adjustment screw on the carb isn't holding the throttle open too far.
