Who knows about 5.5 hp governor Honda power??

https://www.partstree.com/models/gx...cack-1000001-gcack-9999999/cylinder-barrel-6/not sure if this is the same version as yours but the basic engine. sounds like the governor has come undone.
had a vertical shaft mulcher that had same start up problem, zero to redline. took apart, if I remember correctly a part was loose or
disconnected from the shaft that went thru the crankcase. Hope the picture/parts diagram helps!