Chainsaw Repair

Hello, i have a stihl 051 av, when i start it, it idles ok, but then it takes off and high idle  for about 10 seconds then dies. I have tryed to ajust the carb and it still dose it. i think its an air leak, but not sure where. i really want to get this saw running, but not too use, its too big and its a classic...HELP....

How would i do that and where is it on a stihl? is it in the same place as on a husky? in the fule tank?

Go through the fuel system correctly, that old beast deserves to be fixed correctly!!!

Pull and rebuild the carb, check all hoses, connections, gaskets on all of the blocks between the carb and block, impulse.
But before buying anything, after you have the carb off, go ahead and pull the muffler and look at your piston condition, that will
tell you your next step.
When you have the carb apart, you will likely see a wad of snuff in the screen, that would be the remains of your fuel filter insert,
so you will need a new fuel filter, remove the spring/lever/needle, and hold the bare carb body up to a light and peek through that passage, then blow it out with some air, then look again, and visually verify that it is clear, then blow out the other crud, and rebuild with a new kit.

Looking for air leaks is one of the last things to be doing..........

To clarify Roy's post.  The screw/set screw in the tubing style of vent is pushed in about 3-4 threads, NOT screwed in.  If it is screwed in  the treads will cut into the tubing creating a seal loosing the venting ability.  I found this out the hard way on my 08s.