Ok, as far as the air screw, its on the underside of the carb... on the front closestest to the engine. There's a cutaway on that side of the carb where the screw is up in. I have no idea how many turn in or out I'm at.... basically I just fiddle till the idle was the smoothest, if anything a tad on the rich side. You'll need one of those dinky screwdrivers... there isn't lots of room between the carb and the cases.
Now for the idle speed, on the left side of the carb (As you sit on the bike facing foward) there is a bronze screw right in the center of the top half of the carb. Its small, but its pretty much the only thing there. Getting at it is quite a pain, again a small screwdriver works best.
For tuning in the airscrew and the idle I basically got the airscrew set where I thought the idle was the smoothest and there was the least amount of bog when snapping the throttle wide open. Then the idle was quite a bit higher, so I turned it down some.
The main jet is easier to do that either of those two... and it will make the most difference. Thing pulls as hard as it can now at higher rpms. Changing that just involves first dropping the bowl of the carberator. To do that you have to lossen the clamps, take of the hose from the air box, and slid it around so you can get a screwdriver on all the screws. Yamaha reccomends in the maneul that you disconnect the throttle and choke and pull it all the way out, but I think thats a waste of time, worked fine doing it this way. Then you just take out the old 105 main, and slip in you 110 (For a stock TTR125 anyways) with a pair of pliers to hold the main jet nozzle, and a screwdriver to turn the jet. There's a little pink float that was stuck to the main jet that was in there, just pressed on. It wouldn't stick to the new main jet, but there is a spot for it to rest in the bowl of the carb, lines it up right were it should be during reassembally.
I hope this helps ya with your jetting a little. ITs really worth you time. The maneul is decently helpful too, (at least the pictures) especailly if your like me and want to see how it works BEFORE you rip it apart. ;) Have a good one.