where is the pilot screw located on the carb on the yfz 450?

Answer 1

For future reference, always give "year", "make", engine size and model # when asking questions. We need all of that info to give an informed answer.
Bottom of the carb... ahhhh - just look at the picture:
http://www.yamaha-motor.com/sport/service/servicehome/home.aspx
Click - View Parts Catalog (on the left).
Without knowing the year of your bike, use year 2005
Go to - Carburetor - #63