Well, I tried this on my 86 tercel 4WD wagon, and I think the short answer is "you don't." The aisan carburetor on this model has a lot of little parts rattling around inside it (just like any carburetor, I suppose!) and it's difficult to get back together and have it run right. Plus, it needs to be calibrated to work with the feedback system installed on those vehicles. Mine works more or less, but I'm planning on just biting the bullet and buying a professionally rebuilt unit. I figured that after 150k miles, the car deserves it! Here's a link to a site I found that seems to carry the one I need:
http://www.nationalcarburetors.com/cat-toyotacar.html
I saw some improvement after rebuilding mine, but the bigger problem might be the emission controls that work with the carb. I would consult a manual and check these out before tearing into the carb. Some people are putting Weber 32/36 carbs on the 3AC motor. Check out this thread:
http://tercel4wd.com/invision/index.php?act=ST&f=7&t=1112&s=3348c5c032d030e80de8bb4d27ff2d10
Good luck!