1) Do you have a powertorque engine or a full crank engine? You can lower the rev�s on the full crank engines via the governor slot when the engine is running.
2) Can you tell us what o rings you replaced?
3) Have you checked for a crack in the carby or end cap of the carby? The caps are prone to popping off
4) Have you seated the diaphragm correctly and blown into the governor hose. If the diaphragm is seated correctly little to no air will pass the diaphragm. If you can blow air through the governor hose easily the diaphragm will need to be re-seated. It may need to be replaced if it has gone firm.
5) I assume you haven�t got the governor and decompressor hoses mixed up. Govenor hose (end of the carby cap) goes directly to the governor port on the block. The other port on the back of the carby goes to the decompressor (if one is actually fitted)
Was the mower previously operating ok or have you changed the carby off a different unit. Parts often seem the same but G4 carbies are all slightly different in design.
Worst case you have a leaking bottom seal. Check these items first and let us know how you go.
Bigted might jump in with some additional suggestions however I think I have covered things off.
Put up some photos if you can so we can see the mower and carby.
