With the engine off and the dash lever set to fast, the carb should be spring loaded to full open position.
Bring the dash lever to idle, the carb should be closed against the idle stop.
Possibly the U bolt slipped up above the governor link where it attaches to the rod from the dash lever.
If the U bolt did slip, that is where the full speed RPM is set. Be sure to get it right, don't want a runaway.