Hi StotheH, and welcome to the forum. You've come to the right place for help and advice. Sounds like you've got the basics down pat.
You can blank off the decomp valve very easily by removing it and and replacing it with an old CJ8 spark plug.
I have 2 points i'd like to bring up, 1)which "inlet hose" are you squashing which causes the mower to calm down. 2)have you checked the governor diaphragm is seated correctly, you can do this by sucking on the hose that goes to the diaphragm cap.
A couple of pics of the carby area will help to identify if any of the hoses are misplaced.
Cheers, Ted
