New 03 KDX 220R

Picture this:
Remove electronics from lid
Remove lid from bike.
Remove snorkel from lid.
Drop snorkel in trash can.
Clamp lid lightly in vise.
With 1/2 inch paddle bit, drill about 20 (or 21, whatever it takes) holes in lid.
Re-install lid and electronics.

When washing bike, remove lid, place small trash bag or equivalent size thin plastic over opening and re-install lid to hold plastic in place. This keeps spray that makes its way under your seat out of airbox.

Check the archives - and also check FMF's site. If you went with an FMF, they have a jetting chart that will probably be spot on for average elevation 500-2000 feet. Anything up or down and you may have adjust.

I personally did not want that many holes in box - especially int he lower tray.

Picture this.

Leave the electrics in place.

Remove Snorkle (this eveyone aggrees on).

On the upper level of the airbox lid - drill 7 - 9, 3/4" holes with a paddle bit. After doing the math - it will double the air intake area. I didnt like the idea of having holes in the lower tray area - in MO - we have LOTS of water and water like substances to ride through. A few times after riding - I have mud water pooling int he lower tray portion.

This will not give you quite the airflow but it is a good compromise.

I chunked the whole airbox lid. The KDX does not have zerks. Open up your carb and pull the jets out and verify what is actually in there.... it's free.

Air box: chuck the entire lid assembly. As I was worried about water as well, I just put a few strips of duct tape across the front section of frame over the box and sides to keep excess water out. Relocated electronics box to side of air box; secured with a small zip tie.
Jetting: verify what actually came then adjust. Check the two stickies at the top of this forum, lots of great info there.
More questions: just ask. Lots of good help here.