Small Engines (Lawn Mowers, etc.): stihl saw 015, spark arrester, tank fuel

Question
Hey there Michael,
  I have a very old Stihl 015 saw that doesn't run.  I brought it in
to a shop and they rebuilt the carb and told me it was ready to
pick up.  When I picked it up, it wouldn't start.  I got the feeling
they just wanted to get rid of me and then they told me it really
needed a new carb but it was unavailable from stihl or their
other sources.  I called around and found out it is not available.  
They gave me my money back and offered to buy the saw, Hmm.
  Ok, so I started to mess around with it.  I turned the H and L
clockwise all the way and then backed them out 1/2 turn each.  
The saw started, idled, and kind of ran ok at open thottle.  Then
it ran out of gas.  I put more in but it wouldn't start.  I adjusted
the screws some and got it to idle again but it never ran good at
full throttle.  Then it quit and I was never able to restart it,
although I didn't try very long.
  Does this sound like a bad carb or just someone who can't
properly adjust the settings?
I am sorry I couldn't find any numbers on the saw, just the 015.

I really appreciate any insightfullness,
Thanks,
Kreg N.

Answer
Hi Kreg,

The high speed mixture screw is initially set at 1 & 1/2 turns out.  Adjust it to give good acceleration and top speed, while not closing the screw more than you need to.  The low speed mixture screw is set at 3/4 of a turn out.  Adjust that, to give a smooth idle.  The 3rd screw, the idle speed screw, is set to give a low idle speed without stalling.

If setting the screws doesn't help, the carb may be dirty or in need of rebuilding.  I don't know if a carb kit is available.  Also, check the in-tank fuel filter for clogging.  Finally, check the muffler's spark arrester screen for carbon build up.

Let me know how you make out.
Michael