You can temporarily eliminate the decompressor as a suspect by removing it and screwing a spark plug into the hole to close it off. That will make it difficult to pull the starter, but as a quick test, if that cures your idle problem, take a close look at the decompressor. If it makes no difference, reinstall the decompressor and look elsewhere. An air leak is a likely suspect, and on Powertorques those usually come from intake pipe or crankcase (i.e. underneath the starter) O ring leaks. Once you've eliminated the decompressor and the O rings, the carburetor seems the most likely problem. However so many people who work on G4 plastic carburetors end up cursing and rolling across the lawn biting themselves on the backside, it might be best to try the decompressor and O rings first.
