Engine running away after carb rebuild....

Does a 1920 even have an internal return spring..NO ITS DOESN'T. It actually has a default spring that opens the carb via the accelerator pump linkage. Make sure your linkage is set up with a return spring that can overcome the accelerator pump spring and the carb is fully closed. That is the strangest design as if you lose your throttle linkage/return spring, the carb will go ~40% open!