If you do a search on Google and look for Luis Salas. He is Mr. Walbro (so to speak) I learned this from RCIGN1 and have personally talked to Mr. Salas. He also has written a couple of articles on how these carbs function and how to tweak them. Unfortunately some of the information given in this thread is not correct and some is right on. I suggest everyone read these articles, then there will be no doubt.
If I can find the link I will post it.