Dear god people. Would it kill you to just answer the question? If everyone asks this, and they always get told to search, the first 300 results are going to be useless because they'll all say, "You should search." If it bothers you that much, you could just make a word document, write up answers to the 10 most frequently asked questions, end it with "USE THE SEARCH FUNCTION," save it as _Going faster for noobs_ (or something more derogatory if that makes you feel more manly) and copy and paste it every time you see this stuff asked.
That being said, I'm not an expert on any of this by any stretch of the imagination. I'll try to answer as best I can, but you should verify it with searches or with what people respond. I trust people will point and laugh and tell you the right answer if I fuck this up, so here goes:
Yes, if you're going to get a Bi-turbo you should get a bigger jet. I think I remember reading somewhere that the jet controls how much fuel leaves your carb (and goes into the engine) but I could be making that up. Either way, it controls the fuel in the system ... somehow. There's a diagram here if that helps you piece anything together (that's assuming you've got the Dellorto). As for jet size, that really depends. You want one that's bigger, but not so much bigger that you four-stroke or lose performance. Find out what size you've got right now, and buy a range of larger sizes. Start big and work your way down until your plug chops look good. A performance air filter would probably enhance your speed as well, but I've heard of people using pantyhose or drilling holes in things too, so I dunno. If you're looking for jets, try treats -- great prices, ships at the speed of light, and you won't get raped on shipping charges (it's a miracle!)
Yeah... read through this too: