Here is the owner manual:
http://www.stihlusa.com/WebContent/CMSFileLibrary/instructionmanuals/FS36_Manual.pdf
bigted, as I read the manual, the mixture screws have very little effect.

See this instruction file:
http://www.ehow.com/how_7537113_adjust-fs36-stihl-weed-eater.html
Like the owner manual, they expect it to start and run with the screws anywhere from right in to right out. If the machine won't start, and you have spark and compression, it seems likely you'll have to go through the procedure for diagnosis: try a spoonful of fuel in the spark plug hole, and if it starts and runs briefly, you know the carburetor is not delivering enough fuel (or it needs choke). If it continues to run, fiddle with the choke until it warms up, then try to adjust the mixture while it's running. If it runs and stops when primed that way, even with choke, you have to go through the procedure: check the fuel pickup, check the primer, strip the carburetor, replace diaphragms if necessary, and clean it. I haven't been able to find a free service manual for the FS36, but if you post the carburetor make and model we can probably find the manual for that.