I don't remove the carburetor. I just loosen it enough to turn it to the side just enough to allow access to the float bowl screws with a small screw driver. No need to remove all that plastic.

The picture of the two pilot jets above: the one on the left is a series 26, the right one is a series 21. The 400EX carb actually takes a series 26 but a series 21 will work.

I'm with 400exrules about the float bowl screws. I actually replace nearly every screw on the carb with allen head bolts. That way it's easier to get to them with a ball-end allen wrench. This really helps when changing the needle. You have to be careful about overtightening though. They make those philips head screws soft on purpose. The idea is that the screw head will strip before you can damage the much more costly carb body.