I have spent a lot of time searching this forum for tips and explanations on the problems with the '06 YZ450 jetting being too lean. I think I am more confused then when I started. Why would these engineers design a technically advanced bike and sell it with jetting, that according to what I have found here, no-one uses. I want to take care of a brand new $7000.00 purchase but am not really sure what the correct route to go is. I know that members here come from every part of the country with temperature and altitude all being different. I ride in southern California where the temp is usually between 60 and 100 and altitude under 4000 feet. Would the 170 main and 48 pilot be the correct choice for these conditions or should I try a different choice? I know this subject gets beaten to death, but for some this is a whole new animal to deal with, so I appreciate any helpful info.