I'm not real sure about the 450 carb, but on most carbs the pilot screw or the air screw is located on the bottom, toward the front of the carb.
That's probably the drain for the bowl.i just took it out for a run and it seems just a little bit better not much. i didnt mess with the air screw yet. the only screw i see is on the left side of the carb under the fuel line and when i unscrew it, fuell leaks out from one of the vent lines below it
Yeah, I agree with Red. All the mixture screw is for is to get a smooth idle.You're stll not jetted right. the air/fuel screw only effects the idle. It won't do anything for your rpm range.
Try going to the next step up on the clip, see if that helps or makes it worse. You may need to go up on the pilot.