Change the pilot/slow jet from the stock 52 to a 45. Removing the air box lid compensated, but then you were probably lean at WOT. The excess fuel from being rich at idle will take a little while to burn off then the piston would be next. With the idle to 1/4 cleaned up, it will come off idle very crisp. After that do a plug chop and you will probably find you are borderline on the main. If you do the air box mod you asked about in the other thread, you'll probably want to be 2-3 sizes up (148-150) on the main and raise the needle (lower the clip) one position.