Small Engines (Lawn Mowers, etc.): wont run when hot, internal passages, lean condition

Question
My Toro will start but when it gets hot the throtle adjustment becomes irratic. It fluctuates from super high RPM to low and then will stall. It seems that the high RPM is very high and not governed and it will only slow down if I put the choke on.
What do you think this could be? Any help is appreciated.
Paul

Answer
This indicates the carb is dirty inside because the high RPM is caused by a lean condition (carb cannot supply enough fuel) then it dies.  The choke helps because the carb will draw fuel from the low speed circuit in the carb (which isn't blocked).  You need to thoroughly clean the carb, including pushing a piece of tag wire through all of the internal passages.  Hope this helps.