Search for "Stihl FS45 parts diagram" with Google.
Apart from that, I've found the local Stihl agents are pretty good and approachable. Mine printed off a couple of pages from the service manual for my strimmer, which I guess they weren't supposed to and the service tech fished a missing washer out of his junk box FOC. He was interested to see such an old strimmer turn up.
Done that, no luck - easier to find schematics for the B52 bomber.
Well I did find one site in Spanish/Portugese that had schematics for other model Stihl brush cutters - not quite similar to my throttle trigger but it gave an idea.
The cable was knocked off the butterfly but I found there was a spring missing in the trigger mechanism. Dropped on the floor when I dismantled it.
Happy days - it's all together now and I started it up last night. Think the carburettor needs some cleaning or rebuild but no rush.
On most carbs ther are two screws usually marked H and L for the high and low sped mixture. Newer carbs have caps over them to limit the travel (emissions crap.)
Usually you can adjust them unless the carb is real plugged.