Small Engines (Lawn Mowers, etc.): Starting Trouble, internal passages, carberator

Question
I have a walk-behind lawnmower that one day suddenly quit working. It seemed to want to start up but then quit right away. This was about a year or more ago. I cleaned the valve and piston tops off the other day. Cleaned and checked the spark plug for a spark. I also cleaned the carberator as best I could. I tried adjusting the one screw it has, I think, that can be adjusted. But it won't start, and it rarely begins to fire either, although it one spot with that screw it seemed to try to start, at least. I cleaned the gas tank and put fresh fuel in, as well. I cant think of what else it could be.
ANY help apprecitated,
Arthur

Answer
The initial setting for the mixture screw should be 1 1/2 turns out from lightly seated.  If it starts and dies out it's likely there is still debris in the carb and it will need to be cleaned thoroughly.  This includes pushing a piece of tag wire through all of the internal passages and replacing any suspect diaphrams, gaskets or o-rings.  Hope this helps.