I'm away from my summer residence for several more months.....I do not have my service manual with me....however:
I believe something is possibly keeping the connection / linkage from the carburetor to the GOVERNOR in the full FUEL / full RPM mode:
Check for signs of a broken SPRING and or any connections as to the carburetor that may have become disconnected:
With engine not running......have a helper apply full throttle, visually watch all connecting components...then move throttle to min speed...watching all connecting components. Disconnect all connecting linkage at carburetor that is associated with the Hand throttle and the Governor.
Check to see if throttle shaft in Carburetor can be opened and closed freely by hand....CCW...CW...CCW
The throttle shaft should have a "U bolt" / "U Clamp"that attaches a lever to the throttle shaft at some point above the generator.
Check that "U bolt" / "U Clamp" has NOT allowed controls arm to rotate on shaft.
With nothing attached to REACTOR ARM (REACTOR ARM is attached to INTERNAL GOVERNOR WEIGHTS with linkage to carburetor,REACTOR ARM is part of Timing gear cover) try moving the REACTOR ARM FWD and AFT.
If there is no movement FWD or AFT on the REACTOR ARM, POSSIBLY the GOVERNOR FLY WEIGHTS have JAMMED on the CUP MECHANISM that applies force to the inner end of the REACTOR ARM?
See picture of Governor....located inside Timing cover.