I have a 2007 YZ450F and I have been riding it for about 4 months. When the bike is in very low RPM, like when I take off from a stop, the bike is very chattery (if that is a word) . And it also bogs down really bad at low RPM. I rode my brothers CRF450 and it did not have this problem. Do you have any suggestions. By the way, I have a a White Bros XCR exhaust and the bike is jetted 168 and 45. Besides that the bike is stock. I do routine maintenance. I usually ride in the low desert in California around 3000'.