The pilot air screw and pilot jet affects carburetion from idle to around 1/4 throttle.
The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle.
The main jet controls fuel flow from 3/4 thru full throttle.
The pilot air/fuel mixture screw can be adjusted while the bike is idling and then test run. If the engine is running poorly just off of idle, the pilot jet screw can be turned in or out to change the air-fuel mixture. On our carburetor, the pilot screw is located in the front of the carburetor, which regulates the fuel mixture. The mixture will be leaner if it is screwed in and richer if screwed out. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs. You should be somewhere between 2-4 turns.
I have airbox lid off, baffle out, GYTR jet kit: 165 main, 45 pilot jet, 4th clip on the needle, and 2 1/4 turns out runs great. Took a couple of hours to get it right, buy running up and down the street. The key is to check the spark plug each time. Black too rich, white too lean. Every YFZ450 is different so try only one change to the carbuertor at a time. Goodluck. I mainly ride at Glamis. Elevation: sealevel.
How do like the zip-ty screw? Easy to use and to get to the pilot screw