I have a 98 XR400, stock exhaust, snorkel installed, stock air filter (I think), and stock carb. When I'm about 75% throttle the bike bogs real bad, then as I go past the bogs goes away then returns again at wide open throttle. The main jet is 158 and pilot is 58. And ideas? I've been told to go to a lower # main jet and lean it out. Suggestions?