I "will" start racing in AZ too, soon, and my bike hasn't had these problems. Where do you race at? what tracks? I don't think I've seen a yfz yet with a number 17? I can't remember, but if your local, and going to be racing at a race that I'll be attending I'll come over and try to give you a hand.
Anyways on your problem, chec your whole intake from the filter (making sure it's clean) to the intake boot, (nothing obstructing it?) and your carb too. I'm running a 168 main with a JD jetting blue needle on clip 3 and a 45 pilot with the fuel screw turned out 2 1/4 turns. My bike seems to run excellent. Check your plug to make sure your not running lean, or too rich. Also make sure there is no water in the plug cap, and plug hole. If all that is fine, then I'm stumped....lol
let us know what happens.
Also this section is for site comments, not comments on the YFZ, so please make sure you post in the right sections, so more people veiw your threads. Thanks