i spend six month pissing about with the 250tm on the flat track, where it went dead in the top end every time, and was told it was lean, the plug was as you say coloured, but niether here nor there, it turned out it never got on the pipe and therefore never got to show its true coluron the plug.
I was incorrectly using a #270 like in the yamaha 250 only to find out it was supposed to be #190 ? Based on that i would be staying on the jet you have that works and taking a couple either side with you, when you get there in the practice session you will see how long you will need to be on full main and with it wide open on a flat track it will expose itself in no time, unlike a mx or back yard/road run. I would do your runs on a richer needle clip so you change the overlap onto the main much latter, (incase that hole is just the overlap)
It takes about 30 secs to rejet, i would just leave it till you run it on the track, unless its a clear, white plug your not anywhere near lean yet and 2 laps wide open with a chop will give you every thing youll need when you are there.
From my experiance so far on these piston ports they seem to run rich anyway compared to the reed. And dont forget to keep your oil mix measured ther same, more oil will lean out your mix, so keep it static if your chasing jets. I think all will be revealled at wagga, too rich and it will just die in the arse. sit tight, chop at the track.
