Sorry I'd fallen off this thread.
IMO the key to jetting these bikes is all in the needle. A rich pilot will burble just off idle and a lean will give poor response. A rich main will burble up at WOT and a lean will fall a bit flat. The needle is the key. It covered almost the entire rev range and has the most variables. It also overlaps both previous mentioned circuits.
I think the older bikes prefer to run a bit richer than the new. I would definately suggest spending some coins. Get an NEDJ and a N3EJ, both should be happy with around a 42 pilot. NExx 172/175 main, N3xx 178/180. Start with the clip in the middle. If you experience more burbling at 1/4 throttle than you are happy with lift the clip 1 pos and try again. Shouldn't cost much more than $30 in parts.
You could probably borrow a N3EJ/N3EW off a mate if you know anyone with a YZ250
