Lots of idle........

You'll know when you're too lean: You'll get hesitation when you hit the gas hard from an idle. Also, if you're too lean, the bike will scream like hell when you start up cold with the choke on. If you haven't had either symptom yet, go another step leaner. You can't hurt anything otherwise.

My experience says that it won't matter what pilot you use...if you downhill for much time at all, you're going to get a 4-stroke response at the bottom.

Oh..I don't mean like a 4-stroke..but a firing-every-other-time blubbering goober.

OK..maybe I DO mean 'like a 4-stroke' after all? ;)

Anyway...a needle change will cure any plug load-up troubles. Yes..I know you've done some needle changing..but I'm talking about a complete profile change....like a 'C' or even a 'D' series needle.

A better plug does matter. An 'EG' plug will work better in marginal situations than the 'ES' does. No, it's not a substitute for proper jetting, but will resolve spark problems in, as said, marginal situations.

With either a CEL or DEK on my bike (keep in mind it's an rb carb with a #7 slide), I can go downhill as long as I want (or have to)..and at the bottom is nothing but instant throttle response..not a 4-stroke burble nowhere!

CC just gave you the correct answer, but to get you immediately further down the road (if you ride at "normal" elevations) a 42 in the pilot should work fine and give you better--but not perfect response!

Yep. I didn't mean to imply that downsizing the pilot was an error.

It's not.

42 certainly isn't out of line.

I use a 40 even below sealevel AND in the sand. Not a whole lotta low speed stuff in that situation...and what someone else runs has nothing to do with you...but just fyi anyway.

Cheers!