air/fuel adjustment?

I have an ST155 trimmer. I am trying to get it running again. It wants to start, but only runs for a split second if you have choke in the correct position. There are three positions and not sure what the procedure is.I know you put it on full choke when cold, but from then on it is guesswork. To compound the problem, the air fuel valves need adjustment I believe. Do you have a complete procedure for doing all of this?
I would appreciate any help you can give.
Thank you.

Herb
July 2009