Small Engines (Lawn Mowers, etc.): Craftsman engine tuneup, sears craftman, adjustment screws

Question
I have a 8 years old Sears Craftman 4-cycle engine mower, model no. 944.366180(or 143.965002 which also stated in the manual).  I've got it tuneup last year, but the same problem come back again.  That is hard to be started, once started running not smooth and stalled easily.  I have checked the plug and I can find black oily substance on the electrodes.  After cleansing it, it can be started more easily but still seems can not run in full power.  My question is: should I do anything on the two adjusting screws on the left side of the engine?  What are they and how should I adjust them?

Answer
Mixture adjustment screws (not the idle speed screw) should be set to 1 1/2 turns out from lightly seated as a starting point.  If this doesn't correct the problem, you need to investigate if the air filter is clean and if there is an issue with the needle, seat or float in the carb causing the engine to flood.  Hope this helps.