Small Engines (Lawn Mowers, etc.): McCulloch Chain Saws, mcculloch chain saws, air fuel mixture

Question
I have a McCulloch Chain Saw that belonged to my father. I've put in new plug, fuel and chain oil. Clean air filter.
I'm having trouble keeping it running. It has 3 screws next to the choke labeled lo, hi and idle. I've ajusted then and got it to start but never run for longer that a few munites and only if I stay on the throttle. Is there a starting setting for each of these screws like in all the way and out so many turns? I'm pretty sure what the idle screw does but have no idea what the other 2 are. Any help?

Answer
 Hello Jim:

 The Screws you are Asking about are the Air/Fuel Mixture Screws. The Carb on this Chainsaw Needs Rebuilding. The Problem you Described is Common when Fuel Mix is left in the Tank and Carb over Long Periods of Time. Have the Carb Cleaned and Rebuilt. It will Work fine then. Hope this helps.

 Good Luck

 Respectfully

 John