Small Engines (Lawn Mowers, etc.): mower repair, murray riding mower, internal passages

Question
i have a murray riding mower with an 11hp b&s engine.  it is pretty old ,reasonably well cared for.  recently it started surging and losing power under load.  my guess is the carb, but that is about as smart as i get.  other than spraying some cleaner  or adjusting the screw at the bottom of the carburetor(how many turns out?)do you have any advice for a technotard like myself?  thank you for any help you can offer.  

Answer
This is an indication that the carb needs to be cleaned. When it tries to rev up, its fuel demands increase and when the carb can't meet them (due to blockage) the engine dies down and the governor responds and the cycle repeats. The high speed mixture screw on the bottom of the carb should have an initial setting of 1 1/2 turns out from lightly seated.  If adjustment doesn't help, the carb will need to be cleaned thoroughly, including pushing a piece of tag wire through all of the internal passages.  Hope this helps.