Before you start worrying about carburettor problems, suggest you check that the fuel cap is properly vented. Remove it and let the engine run. If it doesn't die after 5 mins, replace the cap.
Top the tank right up before trying this.
There is no choke as such on any version of this mower that I've seen. How old is it, and what engine is fitted?
phil_saunders(a)bigfoot.com
Phil Saunders
October 2012