Jetting
I have a 2001 KTM 520 MXC and I tried the jetting recommendations given by James Dean. I went with a OCEMN needle, third position from top, and a 160 main jet. It now runs great, off idle hesitation is gone and it pulls strong. I ride at sea level, current temp. is upper 70's to mid 90's. I recently went to Colorado, I did not change the jetting, and the bike ran great. I was riding from 7000 feet to 12,700 feet, 50 to 70 degrees. When the temp goes down here in winter, I will probably change to a 162 main jet for the colder temp.
I got the needle from Carb Parts Warehouse, Sudco may also have them.