Hello all. New person here. I have a 2008 400ex that I recently put an hmf slip on exhaust on along with a uni air filter and removed the airbox lid and snorkel. Hmf recommended a 42 pilot jet and 175-180 main jet with this set up. After installing a 42 pilot and 180 main I adjusted the mixture screw to 3.5 turns out. Made sure the carb was clean while it was out. Now the idle is rough and misses occasionally but it runs fine under WOT. It starts really hard too. Spark plug is completely white. I live around 1000ft altitude. What could it be? Thanks in advance!