It hangs down into the fuel bowl of the carburator, so to get a good look at it, turn the carb upside down and remove the bowl. You'll be staring right at it. Its a brass thing that looks kinda like a thick brass flat-headed screw with a hole in the middle.
Oh, and mind that when you turn the carb over that you don't pour fuel all over yourself. Gas stinks and it won't come off your hands or your carpet.
I dunno what the stock jet is, but there should be a number stamped on the jet, probably between 70 and 90.
The oil injector tube is just kinda plugged onto the nipple on the carb. If its stuck, you might try loosening it by placing your thumbnail between the edge of the tube and the carb and pull outward gently to break whatever goo-seal is between the hose and the nipple. You may try a little spray carb cleaner if you're feeling brave. I dunno if that'll melt the hose or not tho.
I can tell you that you can get the aluminum head off without too much effort. Just unscrew the nuts on the head bolts and pull carefully. Be carful not to tear the little lead gasket between the head and iron block. Sure, you can order a new one at your local motorcycle shop, but why? If you don't tear it, it can be reused.
I haven't figured out how to get the iron block off yet (mine's stuck), but I'm trying to get a fella around here to tell me, so I'll let you know if I find anything out.